In this work, the effects of reclaimed sand additions on the microstructure characteristics, mechanical properties and fracture behavior of furan no-bake resin sand have been investigated systematically within the temperature range from 25 to 600 ºC. The addition of 20%-100% reclaimed sand showed dramatic strength deterioration effect at the same temperature, which is associated with the formation of bonding bridges. Both the ultimate tensile strength (UTS) and compressive strength (CS) of the moulding sand initially increase with the increase of temperature, and then sharply decrease with the further increase of temperature, which is attributed to the thermal decomposition of furan resin. The addition amount of reclaimed sand has a remarkable effect on the room temperature fracture mode, i.e., with the addition of 0-20% reclaimed sand, the fracture mode was mainly cohesive fracture; the fracture mode converts to be mixture fracture mode as the addition of reclaimed sand increases to 35%-70%; further increasing the addition to 100% results in the fracture mode of typical adhesive fracture. The fracture surface of the bonding bridge changes from a semblance of cotton or holes to smooth with the increase of test temperature.

Effects of Sc addition on the microstructure and mechanical properties of cast Al-3Li-1.5Cu-0.15Zr alloy were investigated by microscopy methods and tensile tests. With the addition of 0.15 wt% Sc, the grain size of studied alloy in as-cast state decreased from 120 µm to 30 µm and did not grow obviously after two-step solution treatment (32 h at 500 °C+24 h at 560 °C). After aging at 175 °C for 32 h, the elongation (EL) of Sc-containing alloy reached 5.5%, which increased by 83% compared with Al-3Li-1.5Cu-0.15Zr alloy. The key factors for improvement of comprehensive mechanical properties in Al-3Li-1.5Cu-0.15Zr-0.15Sc alloy could be summarized as follows: grain refining, size reduction of δ’ phases and the precipitation of core/double-shell Al3 (Li, Sc, Zr) composite particles.

•Microstructures-property relationship of cast Al-3Li-2Cu-0.2Zr alloy with different Mn addition was systematically studied.•The Mn addition reduced the strength of Al-3Li-2Cu-0.2Zr alloy during ageing.•The alloy ductility exhibits a complex behavior after Mn addition in various ageing stage.•The optimized Mn addition into Al-3Li-2Cu-0.2Zr alloy was 0.3 wt.%.In this work, the influences of Mn content on the microstructures and mechanical properties of cast Al-3Li-2Cu-0.2Zr alloy were investigated. The results showed that with the increase of Mn addition, the as-cast grain size was gradually reduced, and the primary Al20Cu2Mn3 phase was formed in as-cast higher Mn alloys (0.8Mn and 1.2Mn alloy). The formation of Al20Cu2Mn3 dispersoids can restrict the grain growth during solution treatment, but decrease the number density of Cu-rich precipitates during ageing treatment (mainly T1-Al2CuLi) because they consume the solute Cu available for precipitation. The tensile property results showed that Mn addition had little effect on the yield strength (YS) but a detrimental effect on the ductility of the as-quenched alloys due to the presence of Al20Cu2Mn3 dispersoids and/or primary Al20Cu2Mn3 phase. With increasing the Mn content, the YS of ageing-treated alloys was continuously decreased, and the highest elongation of 3.5% was obtained in 0.3Mn-bearing alloy after ageing for 32 h at 175 °C. From the comprehensive consideration of ductility and strength, the optimal Mn addition in cast Al-3Li-2Cu-0.2Zr alloy was 0.3 wt.%.

The effects of solution heat treatment and aging on the microstructural evolution and mechanical behavior of a squeeze-cast (SC) Mg–10Gd–3Y–0.5Zr (GW103K) alloy, processed using various applied pressures (e.g., 0.1, 40, 80 and 160 MPa) were systematically investigated. Our results show that, after solution heat treatment, secondary phases and pressure-induced dislocations are dissolved in the matrix of the squeeze-cast alloys. Moreover, subsequent aging heat treatment leads to an increased age-hardening response relative to that in squeeze-cast GW103K and this trend increases with increasing applied pressure. The room temperature tensile test results show that the yield strength (YS) for the squeeze-cast alloy in the as-cast, the as-T4 heat-treated and the as-T6 heat-treated states increases with increasing applied pressure, from 0.1 to 80 MPa, and remains relatively constant when the applied pressure is increased to 160 MPa, whereas the ultimate tensile strength (UTS) and elongation-to-failure (Ef) increases continuously with increasing applied pressure. The measured increases in YS and UTS (or Ef), are discussed in terms of the mechanisms that govern the evolution of microstructure in squeeze-cast GW103K, paying particular attention to gain size and porosity.

•Formation of θ′ (Al2Cu) was suppressed and S′ (Al2CuMg) phase was introduced with minor Mg addition.•Precipitation of T1 (Al2CuLi) plates was influenced by competition with the S′ phases.•Increasing of δ′-precipitate-free zones (PFZs) width with isothermal ageing time was observed in detail.•Precipitation of T1 phases caused the anomalous decrease in conductivity.The microstructure, electrical conductivity and mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy during heat treatment were investigated. The results indicated that a population of secondary phases enriched along grain boundaries in as-cast studied alloy, most of which dissolved into the α-Al matrix after solution treatment. Profound enhancement in mechanical properties of the studied alloy was obtained after T6 heat treatment. TEM observations revealed competitive precipitation of T1 (Al2CuLi) and S′ (Al2CuMg) phases during ageing, while no θ′ (Al2Cu) phase was observed. The anomalous decrease in conductivity observed during ageing was attributed to the precipitation of T1 phases. Fine δ′ (Al3Li) particles were homogeneously distributed after quenching, gradual coarsening of which was observed with prolonged ageing time. As ageing proceeded, the δ′ coarsened and δ′-Precipitate-Free Zones (PFZs) developed, resulting in diminishing ductility observed from as-quenched to peak-aged state. Precipitation and continuous coarsening of T1 phases kept on at the expense of gradual δ′ dissolution. The improvements of ductility observed in over-aged samples arose mainly from the presence of T1, S′ phases, Al3(Li,Zr) composite precipitates and progressive δ′ dissolution. Moreover, continuous coarsening of T1 and S′ phases contributed primarily to the strength loss in over-aged studied alloy.

In this study, the effects of processing parameters (such as pouring temperature and mould pre-heating temperature) and flame-retardant content on the microstructure and fluidity of sand-cast magnesium (Mg) alloy Mg-10Gd-3Y-0.5Zr (GW103K) were systematically investigated. It was found that the increase of pouring temperature leads to coarsened microstructure and decreased fluidity of sand-cast GW103K alloy. Increase of mould pre-heating temperature incurs coarsening of as-cast microstructure and increase of fluidity. The addition of flame-retardant into moulding sand has a negligible influence on the microstructure of sand-cast GW103K alloy. With the increase in flame-retardant content, fluidity of the alloy initially increases and then decreases. The optimized process parameters and flame-retardant addition were obtained to be pouring temperature of 750 °C, mould temperature of 110 °C, and flame-retardant addition of 1%. The fire retardant mechanism of moulding sand was determined.

•Cast Al-3Li-1.5Cu-02Zr alloy with low density of 2.48 ± 2e − 3 g/cm3 was systematically studied.•Non-spherical δ′ particles and T1 precipitates of very large aspect ratio were observed.•A few of θ′ precipitates of much large aspect ratio were visible in the OA temper.•A good mechanical properties with UTS = 382 MPa, YS = 307 MPa and EL = 2.9% was obtained after heat treatment.The microstructures and mechanical properties of cast Al-3Li-1.5Cu-0.2Zr alloy during heat treatment were investigated. The results showed that large amounts of secondary phases distributed along grain boundaries in as-cast state, and most of them dissolved into the α-Al matrix after solution treatment. The alloy had a very strong age-hardening response with the peak-hardness that was more than double for the as-quenched. TEM showed much fine δ′ (Al3Li) particles were homogeneously distributed after quenching, and long δ′ phases were observed during ageing. Fine T1 (Al2CuLi) precipitate was visible after ageing for 8 h at 175 °C, and both its number density and size increased with the increase of ageing time. Apart from δ′ and T1, θ′ (Al2Cu) phases of large aspect ratio were precipitated in the over-aged condition. As the ageing proceeded, the δ′ particles coarsened and the Precipitate-Free Zones (PFZs) developed, resulting in poor ductility and premature failure. The studied alloy was largely strengthened by the δ′ phase during ageing. After ageing at 175 °C for 32 h, a good mechanical property with ultimate tensile strength (UTS) = 382 MPa, yield strength (YS) = 307 MPa and elongation (EL) = 2.9% was obtained.

The primary phase evolution of ADC12 aluminum alloy rheo-processed by mechanical rotational barrel system was studied by differential scanning calorimetry (DSC), optical microscopy (OM) and scanning electron microscopy (SEM). The semisolid slurry analyses show that the solid fraction of ADC12 aluminum alloy increases from 0.38 to 0.43 while the roundness decreases from 0.45 to 0.38 with increasing the rotational speed from 30 to 120 r/min. When the pouring temperature decreases from 620 to 580 °C, the primary α(Al) morphology changes from spheroidal to rosette-like. Besides, the average particle size of primary phase and solid fraction increase with the decrease of pouring temperature. By rheo-diecasting process, the components with fine, spherical and uniformly distributed primary α(Al) particles were obtained, and the best microstructure was contained at the pouring temperature ranging from 595 to 605 °C. The rheo-processing feasibility of ADC12 aluminum alloy can be explained by the grains controlled growth theory, and the semisolid slurry obeys the Mullins–Sekerka criterion when solidifying in the high pressure die casting machine.

Dry wear behavior of the rheo-casting Al–16Si–4Cu–0.5Mg alloy was investigated by micro-scratch and dry sliding wear tests. Analyses of the microstructure, scratch grooves, wear tracks, worn surfaces and wear debris of the alloy were carried out by optical microscope and scanning electron microscope. The microstructural analysis showed that via rheo-processing, the primary Si was refined and rounded, eutectics dispersed more homogenously, and even the skeleton AlFeMnSi phase was fragmented into facet shape. Micro-scratch test showed that the microstructural refinement resulted in better wear resistance. Dry sliding wear test revealed that the rheo-processed sample exhibit obviously superior wear resistance because of the microstructure improvement. The dominant mechanism in mild wear condition is abrasion, but it turned to adhesion and oxidation in high applied load and fast sliding velocity conditions.

In this study, the compositional dependence of the age hardening response and high temperature tensile properties of the Mg–xGd–3Y–0.5Zr (x=3, 6, 10, and 12 wt%) alloys are investigated. The amount of cuboid-shaped phases and β′ precipitates increased significantly with increasing the Gd content. The Mg–10Gd–3Y–0.5Zr alloy exhibited the maximum ultimate tensile strength at room temperature, while at higher temperatures the Mg–12Gd–3Y–0.5Zr alloy exhibited the maximum yield strength and ultimate tensile strength. The yield strength and ultimate tensile strength of the Mg–12Gd–3Y–0.5Zr alloy increased with the test temperature and showed its maximum at 150 °C, and then decreased as the temperature increased further. The Mg–12Gd–3Y–0.5Zr alloy maintained a high ultimate tensile strength of more than 300 MPa up to 250 °C. The superior high temperature tensile strength of the tested alloy is mainly associated with solution strengthening and precipitation hardening of the cuboid-shaped phases and β′ precipitates in Mg matrix. Especially, β′ precipitates can hinder the dislocation movement at high temperature.

The microstructures and mechanical properties of cast Al-3Li-xCu-0.2Zr alloy were investigated. The results showed that Cu addition could slightly refine the grain size of as-cast alloy. Cu element was significantly enriched at the grain boundaries, and Cu-rich intermetallic compounds were formed in the Cu-containing alloys during casting. The peak hardness increased and the time to peak ageing decreased with the increase of Cu content. Cu addition also had a pronounced influence on the precipitation behavior of Al-3Li-xCu-0.2Zr alloys, i.e. the number density, size and distribution of T1-Al2CuLi and θ′-Al2Cu phases. The tensile strength was effectively improved after 2 wt% Cu addition compared with Al-3Li-0.2Zr alloy. A good combination of strength to ductility could be obtained in Al-3Li-2Cu-0.2Zr alloy after solution and ageing 32 h at 175 °C. The precipitation-free zones (PFZs) were developed with the coarsening of δ′-Al3Li particles in the peak-aged (PA) and over-aged (OA) state, promoting the poor ductility and premature failure.

Microstructure, mechanical properties and fracture behaviors of sand-cast Mg-4Y-3Nd-1Gd-0.2Zn-0.5Zr (wt%) alloy in different thermal conditions were investigated. The as-cast alloy was comprised of α-Mg matrix, Mg24Y5, Mg41Nd5 and β1 phases. After solution treatment at 525 °C for 6 h, the eutectics dissolved into α-Mg matrix, leading to a huge improvement of plasticity. Alloys peak-aged at 200 °C and 225 °C exhibit high strength due to fine dense β″ and β′ precipitates. Aged at 250 °C for 10 h, the precipitates in the alloy are coarse sparse coupled β1/β′ phases. A desirable combination of strength and ductility was obtained with 198 MPa in yield strength, 276 MPa in ultimate tensile strength and 7.6% in elongation when over-aged at 250 °C for 10 h. Alloys under different thermal conditions show different fracture behaviors, which are closely linked to the structures of both inner grains and grain boundaries.

•I-phase forms in as-cast Mg–Li–Zn–Gd alloys.•I-phase is broken into fine particles during hot extrusion.•Increase of I-phase content improves the strength of as-extruded Mg–Li–Zn–Gd alloys.Mg–Li–Zn–Gd alloys reinforced with icosahedral quasicrystal phase (I-phase) were prepared by casting and deformed by hot extrusion. The microstructure and tensile properties of as-extruded Mg–Li–Zn–Gd alloys were investigated. It is found that I-phase formed in as-cast Mg–Li–Zn–Gd alloys and was broken into small particles during extrusion. After hot extrusion, both α-Mg and β-Li phases were elongated along the extrusion direction. Dynamic recrystallization occurred in as-extruded Mg–Li–Zn–Gd alloys. Compared with Mg–9Li (L9) alloy, the improvement in mechanical properties especially the tensile strength of the as-extruded Mg–Li–Zn–Gd alloys was mainly ascribed to the formation of I-phase and their volume fraction. Moreover, the finely recrystallized grain structure can also attribute to the strength enhancement of the alloy.

•The precipitation process in Mg–10Gd–3Y–0.8Al (wt.%) alloy has been investigated.•Particles with the 18R-type LPSO structure were observed in the solution state.•Upon ageing at 250 °C, the precipitation sequence is: β″ → β′ → β1 (fcc) → β.•The Al grain-refined alloy has a lower hardness than the Zr refined counterpart.The precipitation process in Mg–10Gd–3Y (wt.%) alloy grain-refined by 0.8 wt.% Al addition has been investigated by transmission electron microscopy. The alloy was given a solution treatment at 520 °C for 6 h plus 550 °C for 7 h before ageing at 250 °C. Plate-shaped intermetallic particles with the 18R-type long-period stacking ordered structure were observed in the solution-treated state. Upon isothermal ageing at 250 °C, the following precipitation sequence was identified for the α-Mg supersaturated solution: β″ (D019) → β′ (bco) → β1 (fcc) → β (fcc). The observed precipitation process and age hardening response in the Al grain-refined Mg–10Gd–3Y alloy are compared with those reported in the Zr grain-refined counterpart.

The microstructures and mechanical properties of Mg–xZn–1.25RE–Zr (x=3.5, 4.2, 5.0 wt%) and Mg–4.2Zn–yRE–Zr (y=1.0, 1.25, 1.5 wt%) alloys in as-cast and 325 °C peak-aged condition were investigated in this study. The as-cast Mg–xZn–yRE–Zr alloys consist of α-Mg matrix, T-phase and Mg51Zn20 phase. For Mg–xZn–1.25RE–Zr alloys, 4.2 wt% Zn addition led to smallest average grain size and better eutectics morphology of discontinuous network, short-bar and island shape. For Mg–4.2Zn–yRE–Zr alloy, increase in RE content gradually refined the microstructure and contributed to more triangular particles and networks. After peak-aged at 325 °C, the strengthening of Mg–xZn–yRE–Zr alloys occurred through the precipitations of rod-like β′1 phases. With Zn content from 3.5 to 5.0 wt%, the strengthening effect first increased and then decreased, with a turning point of 4.2 wt% Zn. The descend of strengthening effects at 5.0 wt% was mainly ascribed to the formation of plate-like β′2 phases and reduced number density of β′1 phases. With RE addition from 1.0 to 1.5 wt%, the strengthening effect increased because of the denser and finer β′1 phases. When x=4.2 and y=1.25–1.5 wt%, the Mg–xZn–yRE–Zr alloy reveals good combination of strength and elongation in 325 °C peak-aged condition, and was chosen as optimal chemical composition.

AZ91–(1–3 wt%) Ca alloys were prepared by direct squeeze casting, in which the melt was solidified under applied pressure. The effects of processing parameters (such as applied pressure and pouring temperature) and Ca content on microstructure and mechanical properties of squeeze casting AZ91–Ca alloys were investigated. The results indicate that the microstructure was refined with the increase of applied pressure, and the mechanical properties were improved. When the pouring temperature was lowered down to near the liquidus, the microstructure was further refined and α-Mg grains turned rosette-like. The negative effect on ambient temperature mechanical properties caused by the addition of Ca into AZ91 alloy was inhibited by squeeze casting. Compared to conventional casting, squeeze casting process can offer AZ91–Ca alloys better mechanical properties, especially in elongation to failure (Ef).

The present study investigated the effect of cooling rate on the microstructure and mechanical properties of sand casting Mg–10Gd–3Y–0.5Zr alloy with a cooling rate range of 0.7–3.6 °C/s. When the cooling rate was increased, the average grain size of α-Mg decreased from 59 μm to 39 μm, the volume fraction of the second phase increased from 17.6% to 24.5%, and the eutectic compound exhibited continuous network instead of coarsening discontinuous network of plate-shaped microstructure. Energy-dispersive X-ray test results suggested that solute content of RE elements (Gd and Y) was low within the area near the grain boundary of α-Mg with high cooling rate, and solid-solution reaction occurred in the sand casting process. In addition, Vickers hardness (HV) testing indicated that HV increased with the increasing cooling rate, and the volume fraction of second phase (V) played a main role in hardness of the alloys. There was a linear relationship between them, the fitting function was HV=1.25 V+63.05, R2=0.9989. Tensile strength test showed that both of ultimate tensile strength (UTS) and tensile yield strength (TYS) first increased and then decreased with the increasing cooling rate. Based on fracture observations, the types of fracture surface characteristics are correspondingly classified into three modes, transgranular, dimple-like fracture and intergranular fracture with the increasing cooling rate.

In this study, the effect of rotating gas bubble stirring treatment on the microstructures of semi-solid AZ91-2Ca alloy was investigated. The semi-solid slurry was produced by injecting fine gas bubbles into the melt through a rotating steel diffuser during solidification, and the samples of semi-solid slurry were taken by the rapid quenching method. The results show that fine and spherical α-Mg particles can be obtained under rotating gas bubble stirring treatment. The process parameters such as gas flow rate, cooling rate and rotation speed have significant influence on the morphology of primary solid particles. After rotating gas bubble stirring treatment, the higher the particle density, the finer and rounder the primary α-Mg particles. The formation of numerous solid particles is due to the combination mechanisms of copious nucleation and dendrite fragmentation.

In this study, the microstructure evolution of semi-solid Mg–10Gd–3Y–0.5Zr alloy during isothermal heat treatment has been investigated. The results show that primary particles coarsen continuously during the holding. Coarsening rate decreases with the increase of isothermal temperature. When isothermal temperature increases from 600 °C to 620 °C, the dominant mechanism for coarsening changes from particle coalescence to Ostwald ripening. Equiaxed as-cast microstructure is beneficial to the semi-solid microstructure after isothermal heat treatment, which brings about the refinement and spheroidization of primary particles, and shortening of holding time. Significant modification of second phases can also be achieved after isothermal heat treatment, due to its unique solidification process. The optimum processing parameters for Mg–10Gd–3Y–0.5Zr alloy in isothermal heat treatment are isothermal temperature of 610 °C–620 °C and holding time of 20–40 min.

The morphology of precipitates and grain boundaries of peak-aged Mg34Y32Nd31Gd alloys under different aging conditions were analyzed by transmission electron microscopy (TEM), and the mechanical properties and fracture behavior of the studied alloys both at room and elevated temperatures were investigated. The β′′ and β′ phases are the main precipitates of the alloys peak-aged at 200 °C and 225 °C, while the alloy peak-aged at 250 °C mainly consists of β1 and β phases. Discussion on relationship between precipitates and mechanical properties, fracture behavior reveals that the precipitates' density, kind and arrangement are the dominating factors influencing the mechanical properties, and the combined influence of grain boundary structure and precipitation hardening determine the fracture mechanism of Mg34Y32Nd31Gd alloys.

The effect of additions of 0.5–1 wt% Al on grain refinement, heat treatment and mechanical properties of Mg–10Gd–3Y (wt%) alloy has been investigated. The additions of 0.6–1 wt% Al showed a dramatic grain refinement effect, which is associated with the formation of the Al2(Gd0.5Y0.5) particles that act as nucleants for α-Mg grains. Compared to the Zr refined counterpart, the Al refined alloy needed to be solution treated at a higher temperature to dissolve the majority of the intermetallic particles. Subsequent ageing at low temperatures led to pronounced precipitation hardening and consequently a large improvement in strength. In the peak-aged condition, the strength of the Al refined alloy is comparable to that of the Zr refined counterpart.

Mg–13Al–xCa (x = 0, 0.3, 0.6, 1.0 and 3.0 wt.%) alloys were designed for semisolid forming, and the effects of Ca content on the microstructures of semisolid Mg–13Al alloys produced via isothermal heat treatment were investigated. The results show that with increasing quantity of Ca added, the average size of solid particles in semisolid slurry has a trend of first increase and then decrease. And the solid particles in Mg–13Al alloy without Ca addition are smaller and more spherical than those in the alloys with Ca addition. These changes in semisolid microstructure associate with the distribution of low melting point phases and the morphology of primary α-Mg phases at as-cast state. The melting temperature of Al2Ca phase in Mg–13Al–xCa alloys is lower than that of primary α-Mg phase. With the increasing of Ca content, Al2Ca phases will become an important part of the liquid matrix in semisolid slurry. Among the semisolid Mg–13Al–0.3Ca, Mg–13Al–0.6Ca, Mg–13Al–1Ca and Mg–13Al–3Ca alloys, the best rheological parameters are obtained for the 3.0 wt.% Ca containing alloy. The optimum isothermal temperature range for Mg–13Al–3Ca alloy is between 515 and 550 °C.Highlights► Al2Ca phase becomes an important part of the liquid matrix with Ca addition. ► The isothermal temperature range for Mg–13Al–3Ca alloy is between 515 and 550 °C. ► The as-cast microstructures greatly influence the semisolid microstructures.

The influences of potassium fluozirconate (K2ZrF6) salts mixture (KSM) on the grain refinement, microstructure, mechanical properties and corrosion resistance of Mg–10Gd–3Y (GW103, wt.%) magnesium alloy were investigated. The results show that an addition of 8 wt.% KSM-2 (50 wt.% K2ZrF6–25 wt.% NaCl–25 wt.% KCl) provides the best combination of fine grain size and the lowest fraction of inclusions for GW103 alloy. The mechanical properties and corrosion resistance of GW103 alloy are improved by KSM-2 addition. The formation of Zr from the in situ reaction between Mg melt and K2ZrF6 is responsible for the refining mechanism of KSM. Compared with the Mg–30 wt.% Zr master alloy, the KSM refiner shows much longer fading time during smelting.

The effects of GdCl3 in flux on the loss of Gd, microstructure, mechanical and corrosion properties of Mg–10 wt.% Gd–3 wt.% Y–0.5 wt.% Zr (GW103K) alloy were investigated. The results indicate that the loss of Gd in the alloy decreased when the melts were refined by fluxes containing GdCl3 additions. Thermodynamic analysis revealed that the decline of Gibbs free energy is the main reason, which slows down the reaction rate between MgCl2 and Gd in melts. In as-cast condition, after treated with 5 wt.% GdCl3 additions, tensile yield strength, ultimate tensile strength and elongation of the alloy could reach the peak value of 201.51 MPa, 154.68 MPa and 2.56% respectively. 5 wt.% NaCl aqueous solution immersion test shows that the corrosion rate of GW103K alloy decreased to 0.437 mg cm−2 d−1 after refined by JDMJ + 5 wt.% GdCl3. However GdCl3 additions have no effects on microstructure and fracture pattern of GW103K alloy.

The influence of Cl− and SO42− on the electrochemical behavior of AZ91D, AZCe2, and AZLa1 was studied. For all alloys, there was a current plateau in the anodic polarization curves in Na2SO4 solutions. In 0.5% NaCl solution, there was a small current plateau, whereas there was none in the 3.5% and 5% NaCl solutions. This indicated that SO42− is less aggressive than Cl−. The range of the current plateau decreased with increasing SO42− concentration. For all alloys, the high frequency capacitive loop in the Nyquist plots decreased with increasing concentration consistent with the decrease in corrosion resistance with increasing Cl− and SO42− concentration.

This paper studies the fatigue properties and fracture behavior of as-extruded Mg–6Zn–0.5Zr and Mg–10Gd–3Y–0.5Zr alloys before and after shot peening. Compared to Mg–6Zn–0.5Zr alloy, Mg–10Gd–3Y–0.5Zr alloy shows higher optimal Almen intensity, and possesses a broader process window. The stress-controlled rotating bending fatigue property improvement for Mg–10Gd–3Y–0.5Zr alloy by shot peening is significantly superior to that of Mg–6Zn–0.5Zr alloy. With the increase in peening (Almen) intensity, the fatigue crack nucleation site of Mg–6Zn–0.5Zr alloy under stress control shifted from the surface to subsurface, and then back to the surface again. Meanwhile, a significantly higher number of fatigue crack initiation sites can be seen as a consequence of overpeening. However, the fatigue cracks of the peened Mg–10Gd–3Y–0.5Zr alloy initiated subsurface at all Almen intensities, showing unchanged crack initiation location with the increase in Almen intensity. The observed phenomenon is related to differences between the two alloys both in the deformation mechanisms during shot peening and the residual stress relaxation mechanisms during subsequent fatigue process. Namely, at present test conditions such as Almen intensity range and high cycle fatigue stress, in the Mg–6Zn–0.5Zr alloy twinning dominates deformation during shot peening and detwinning during fatigue. Comparatively, dislocation slip dominates deformation in both shot peening and fatigue process in the Mg–10Gd–3Y–0.5Zr alloy.Highlights• The as-extruded Mg–6Zn–0.5Zr alloy exhibits a strong twinning and detwinning phenomenon. • Mechanical twinning dominates deformation in Mg–6Zn–0.5Zr alloy during shot peening. • Dislocation slip dominates deformation in Mg–10Gd–3Y–0.5Zr alloy during shot peening. • The two alloys exhibit different fatigue strengthening mechanisms by shot peening.

Microstructure evolution and mechanical properties of the rheo-processed ADC12 alloy were investigated by means of optical microscopy, X-ray diffraction and scanning electron microscopy. Primary dendritic Al of rheo-casting (RC) and rheo-diecasting (RDC) ADC12 alloys are sheared off. The average size, as well as solid fraction of the primary Al increase with descending pouring temperature. The mechanical properties of alloys are strengthened by rheo-processing. Ultimate tensile strengths of RC samples increase with the decrease of the pouring temperature, and reach the maximum in the range from 580 to 600 °C. At pouring temperature of 595 °C, the RDC sample obtains the best ultimate tensile strength and elongation. Great reductions on porosity and primary Al globularization are crucial to the mechanical properties. Relationships of the primary Al size and yield stress are depicted with Hall–Petch equation.