Effects of (Pr+Ce) addition on the Al-7Si-0.7Mg alloy were investigated by optical microscope (OM), energy diffraction spectrum (EDS), X-ray diffraction (XRD) and tensile tests. The results showed that the Al-7Si-0.7Mg alloy was modified with (Pr+Ce) addition. The needle-like eutectic silicon phase developed into rose form and the crystalline grains decreased in size and showed a high degree of spheroidization. When the amount of the (Pr+Ce) addition reached 0.6 wt.%, the mean diameter was 31.8 μm (refined by 50%). The aspect ratio decreased to 1.35, and the tensile strength and ductility reached 192.4 MPa and 2.18%, respectively. At higher levels of addition, over-modification occurred, as indicated by increased grain size and reduced mechanical properties. The poisoning effect of the (Pr+Ce) addition on eutectic silicon and the constitutional supercooling caused by the (Pr+Ce) addition were the major causes of alloy modification, grain refinement, and the improvement of mechanical properties.Fracture graphs of the tensile samples (a) Unmodified; (b) 0.3% (Pr+Ce); (c) 0.6% (Pr+Ce); (d) 0.9% (Pr+Ce)Download high-res image (154KB)Download full-size image

Using coal fly ash slurry samples supplemented with different amounts of Al2O3, we fabricated mullite-based porous ceramics via a dipping-polymer-replica approach, which is a popular method suitable for industrial application. The microstructure, phase composition, and compressive strength of the sintered samples were investigated. Mullite was identified in all of the prepared materials by X-ray diffraction analysis. The microstructure and compressive strength were strongly influenced by the content of Al2O3. As the Al/Si mole ratio in the starting materials was increased from 0.84 to 2.40, the amount of amorphous phases in the sintered microstructure decreased and the compressive strength of the sintered samples increased. A further increase in the Al2O3 content resulted in a decrease in the compressive strength of the sintered samples. The mullite-based porous ceramic with an Al/Si molar ratio of 2.40 exhibited the highest compressive strength and the greatest shrinkage among the investigated samples prepared using coal fly ash as the main starting material.

The optical microscopy, scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) were used to assess the influence of micro-addition of (La+Yb) on the microstructure and mechanical performance of the AlSi10Cu3 alloy in heat treatment conditions. It was shown that the appropriate (La+Yb) addition (0.3 wt.% or 0.6 wt.%) transformed the needle-like β-Al5FeSi phase into Chinese script or spherical α-Al8Fe2Si phase. Eutectic silicon refined the long needle-like particles into granular or round particles at 0.6 wt.% (La+Yb) content. Moreover, the La3Al11 and YbAl3 phases acted as strengthening phases during the heat treatment processing in the alloy with the addition of (La+Yb). Consequently, the alloy with 0.6 wt.% (La+Yb) exhibited an enhanced mechanical properties response with ultimate tensile strength, elongation, and hardness at 69.35%, 113.26% and 23.61% higher than those of the unmodified alloy, respectively. Further addition (0.9 wt.%) of (La+Yb) resulted in the increasing of the black acicular RE-rich intermetallics during heat treatment, which could aggravate the situation of stress concentration leading to deterioration of the mechanical properties of alloy.Morphologies of tensile fracture surface of heat-treated alloys with different (La+Yb) contents (a) 0; (b) 0.3 wt.%; (c) 0.6 wt.%; (d) 0.9 wt.%

The study systematically investigated the effects of master alloy addition containing rare earth elements La and Yb on the microstructures characteristic and tensile properties of AlSi10Cu3 alloy. It was studied by means of optical microscopy, X-ray diffraction, scanning electron microscopy, energy diffraction spectrum and differential thermal analyzer. The results showed that the addition of (La+Yb) obviously reduced the sizes of the primary α-Al phase and eutectic Si particles as well as β-Al5FeSi phase and improved the morphology of the primary α-Al phase and eutectic Si particles. The optimum addition of (La+Yb) addition was 0.6 wt.%. Comparing the 0.6 wt.% (La+Yb) modified AlSi10Cu3 alloy with the unmodified alloy, it was found that the mean diameter, mean area and SADS of primary α-Al phase were decreased by 50.80%, 75.74% and 50.83% respectively; the aspect ratio, size (length) and mean area of eutectic Si particles were decreased by 66.30%, 81.78% and 78.99%, respectively, and the average size of the β-Al5FeSi phase was 16.4 μm. In addition, the addition of (La+Yb) greatly improved the tensile properties of AlSi10Cu3 alloy, especially in the ultimate tensile strength and elongation as a result of the significant improvement in microstructure.Effect of (La+Yb) addition on the length of β-Al5FeSi phase in alloys

•The semisolid structure of in situ Mg2Si/AM60 composite is produced by ultrasonic vibration treatment.•The treatment is more effective in controlling the morphology and size of α-Mg particles when applied at just a few degrees above the liquidus temperature.•Separate mechanisms which appear to be operating in either case are discussed.•The Mg2Si and Mg17Al12 intermetallics dispersed uniformly in the metallic liquid matrix can also be identified as segregated along the grain boundaries of the “smaller grains” from the view of microcosmic.The application of ultrasonic vibration treatment (UVT) produced a nearly non-dendritic and refined semi-solid microstructure of Mg2Si/AM60 composite. The effects of UVT temperature and time on microstructure of the semi-solid slurry were studied. A good semi-solid slurry with average grain size of 75 μm and shape coefficient of 0.53 could be obtained by applying UVT at 620 °C for 60 s, which were decreased by a factor of 17/20 and increased by a factor of 3 respectively as compared to the sample without treatment. The Mg2Si and Mg17Al12 intermetallics are mainly located along the grain boundaries or dispersed uniformly in the metallic liquid matrix with network morphology. Mechanisms involved in the development of microstructure are discussed.

•Sm affected the secondary dendrite arm spacing of Al–7Si–0.7Mg alloy.•The coarse plate-like eutectic silicon was fully modified into a fine branched and particle structure when 0.6 wt.% Sm added.•The tensile properties were enhanced by the addition of Sm.•Sm has marked effects on eutectic temperature and the latent heat ΔHR on remelting behavior.•The morphology and chemical composition of Sm-rich intermetallics were studied.The effects of samarium (Sm) additions (0–0.9 wt.%) on the microstructures and mechanical properties of Al–7Si–0.7Mg alloys have been studied in this article. The microstructures of the as-cast samples were examined by optical microscopy (OM) and scanning electron microscopy (SEM). The experimental results indicated that the rare earth Sm affected the secondary dendrite arm spacing (SDAS) of Al–7Si–0.7Mg alloy. And it was found that Sm had great modification effects on the microstructures of eutectic silicon. When 0.6 wt.% Sm was added to the alloy, the coarse plate-like eutectic silicon was fully modified into a fine fibrous structure; the dendrites of Al–7Si–0.7Mg alloy was best refined. The mechanical properties were investigated by tensile test. The findings indicate that the tensile properties and elongation were improved by the addition of Sm. And a good combination of ultimate tensile strength (215 MPa) and elongation (3.3%) was obtained when the Sm addition was up to 0.6 wt.%. Furthermore the results of thermal analysis reveal that Sm addition had marked effects on eutectic temperature and the latent heat ΔHR on remelting behavior.

The effects of Sm additions (0, 0.5 wt.%, 1.0 wt.% and 1.5 wt.%) on the eutectic Si and β-Al5FeSi phases of ADC12 as-cast alloys were studied by optical microscopy (OM), scanning electron microscopy (SEM) and differential thermal analysis (DTA). The experimental results showed that Sm was an effective modifying agent for the eutectic Si of ADC12 alloy, when 1.0 wt.%–1.5 wt.% Sm was added to the alloy, the coarse acicular eutectic Si was modified into fine particle or short rod structure. Moreover, the appropriate addition of Sm (about 1.0 wt.%) had marked effects on shortening the length of needle-like β-Al5FeSi phase. Whereas, Sm was less effective on modifying the needle-like β-iron to the Chinese script or spherical α-iron phase. The modification mechanism was also discussed.Morphologies of β-Al5FeSi in ADC12 alloys with different Sm additions (1.0 wt.% Sm)

In general, the flow stress models used for theoretic analysis and computer simulation in machining processes are a function of strain, strain rate and temperature during the cutting process. However, these models do not adequately describe the material behaviour in hard machining, where the workpiece material is machined in its hardened condition. This hardness modifies the strength and work hardening characteristics of the material being cut. An approach is presented to characterize the stress response of workpiece in hard machining, accounted for the effect of the initial workpiece hardness in addition to temperature, strain and strain rate on flow stress in this paper. AISI H13 die steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with data collected from published experiments. Therefore, the proposed model can be used to predict the corresponding flow stress–strain response of AISI H13 die steel with variation of the initial workpiece hardness in hard machining.

The many kinds of casting defects such as insufficient pouring, cooling separation, crack, shrinkage and so on were formed in the mold filling and solidification processes, which contributed to the final casting performance. Based on the mathematical models of mold filling and solidification processes, the numerical simulation of AZ91D magnesium alloy automobile plug in pressure die casting process has been done. The filling behaviors at each stage in the filling process were presented. The temperature distributions in the solidification process were obtained, and the positions of shrinkage and slack were predicted. According to the simulated results, an improved scheme is proposed, and its workpiece defects are reduced largely. The predicted results are in good agreement with practical ones.

•The content, size and distribution of nanoparticles affected the true stress of the nanocomposites during thixoforming.•A visco-plastic constitutive model for predicting the thixotropic behavior of the nanocomposites was developed.•The thixotropic behavior of the nanocomposites was well explained by fracture analysis.The thixotropic compression tests of nano-Al2O3 (Al2O3np)/Al7075 composites with different particle sizes and contents and containing a high fraction of solid, were conducted under conditions of 560–590 °C and 0.01–5 s−1, and the microstructures were observed. A visco-plastic constitutive model of nanoparticle reinforced composites for thixoforming was proposed, considering the coupling effects of strain, strain rate, deformation temperature and liquid fraction and presence of nanoparticles, to describe constitutive behavior of the composites under various deformation conditions. Furthermore, the influence of deformation parameters on thixoforming was investigated. It could be shown that the predictions by the developed model were consistent with experimental results. Fracture analysis of the thixotropic compression samples revealed that high deformation temperature or/and high strain rate could prompt continuous uniform distribution of the liquid phase along the grain boundary, causing the formation of a thin liquid film around an approximately spherical grain, accordingly improving thixoformability of the composites with a high solid fraction. Moreover, deformation mechanisms of the composites during thixotropic compression process were discussed.