Effects of Adding Trace Modification Elements and Heat Treatment on the Strength and Toughness of AlSi8Cu2MgMn Alloy

In order to improve the strength and toughness of die casting aluminum alloy, a high strength and toughness die casting aluminum alloy was developed by vacuum die casting, Sr–Ti–Sc–Zr quaternary modification and heat treatment on the basis of AlSi8Cu2MgMn alloy. The effects of Sr–Ti–Sc–Zr modification, solid solution and aging heat treatment on the microstructure and mechanical properties of AlSi8Cu2MgMn alloy were studied by means of optical microscope, scanning electron microscope, X-ray diffraction, transmission electron microscope, tensile test and hardness test. The results showed that the microstructure of AlSi8Cu2MgMn alloy could be significantly refined by Sr–Ti–Sc–Zr quaternary modification, and the eutectic silicon phase could be transformed into granular or branched fibers. The microstructure of AlSi8Cu2MgMn-X (Sr–Ti–Sc–Zr) alloy was more homogeneous, the morphology of primary α₁-Al phase and secondary α₂-Al phase was improved, and the fibrous silicon phase was spherical. The mechanical properties of the alloy were greatly enhanced by precipitation strengthening of θ′(Al₂Cu) and Q′(Al₅Cu₂Mg₈Si₆) phases containing copper. Compared with other reported die-cast aluminum alloys, the die-cast AlSi8Cu2MgMn-X alloy reached a high level of tensile strength and elongation. The best mechanical properties of AlSi8Cu2MgMn-X alloy after solid solution treatment at 450 °C for 3 h and aging treatment at 170 °C for 12 h were as follows: tensile strength 322 MPa, yield strength 198 MPa and elongation 13.6%.