•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.%.

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.

•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.

•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 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.