Development of a novel high strength Al-Si-Cu-Ni alloy by combining micro-alloying and squeeze casting

In this paper, a new type of Al-8Si-1.5Cu-1Ni-0.5Mg-0.5Mn-0.2Ti-0.2Zr-0.2V-0.06Sr alloy (Al-Si-Cu-Ni alloy for short) was prepared by combining micro-alloying and squeeze casting (SC) forming technology, and its microstructure and mechanical properties were investigated. The results show that the average diameter and secondary dendritic arm spacing of α-Al grains in Al-Si-Cu-Ni alloy prepared by SC are 63 µm and 12.8 µm respectively, and the internal pores of the alloy are basically eliminated. Moreover, the eutectic Si and complex second phases (i.e., AlSiMnFe, Al3CuNi and (Al,Si)3(Zr,Ti,V)) are greatly refined and more uniformly distributed in the SC alloy. In particular, the eutectic Si can even be refined to sub-micron or nanoscale, and its average F value (i.e., average shape factor) for eutectic Si in the SC alloy is 0.57, which is 29.5 % higher than that of GC alloy. The as-cast ultimate tensile strength (UTS), yield strength (YS) and elongation of the SC Al-Si-Cu-Ni alloy are 310 MPa, 169 MPa and 3.8 %, respectively. Interestingly, its UTS and ductility are much higher than those of most other Al-Si alloys formed by same method, especially its UTS can even be comparable to that of some T6 heat-treated alloys. The increase in strength and elongation is mainly attributed to a reduction in porosity, grain refinement and improvement in the morphology of the second phases.