Microstructure And Propeties Of Al-Si Casting And Forging Alloy Containing Sc

The addition of Sc to Al-based alloys has been widely concerned and researched due to its obvious function on microstructure and mechanical properties of alloys. A kind of Al-Si casting and forging alloy was prepared based on the composition adjustment of A356 alloy. Adding minor Sc into Al-Si casting and forging alloy and investigating the effect of Sc on microstructure and properties would be helpfull in both theory and practice of developing high-strength and light-weight of Al-Si alloy materials.In this dissertation, five different kinds of Al-3.OSi-0.45Mg-0.45Cu-0.15Ti alloys containing Sc element have been designed. The microstructures and mechanical properties after casting, T6 treatment and deformation for this experiment alloys with and without Sc were investigated respectively by metallographic microscope, field emission scanning electron microscope, energy spectroscopy analysis, field emission transmission electron microscope and universal testing machine. The process parameters of T6 heat treatment and deformation treatment for this alloy were designed after various experiments. The results showed that adding 0.20wt.%Sc into the casting alloy can refine the grain, change the growth morphology from dendritic to fine equiaxed grain, and the average of grain size is 50μm. While the mechanical properties of as-cast alloys also are enhanced, but not very obviously. The fracture mode of as-cast alloys’ tensile bar is mainly brittle fracture. It has a great impact on the mechanical properties of alloy after T6 heat treated with minor Sc addition. The tensile strength, elongation rate, and hardness can reach 304.4MPa, 14.8%, and 104.5HBS after adding 0.2wt.% Sc. The fracture mode of T6 treated alloys’ tensile bar tend to ductile fracture. This T6 state alloy state had better comprehensive mechanical properties, much better than A356 alloy. The microstructure defects of alloy were improved after 15% deformation to this Al-Si alloy, which can improve the comprehensive mechanical properties of alloy, especially the plasticity furtherly. The elongation rate reaches 17.3%, and the plasticity is close to the level of deforming Al alloy for the alloy with 0.2wt.% Sc after small deformation. The fracture morphology of tensile bar is better than that of T6 state alloy after deformation.It can be found that Sc can play a more important role in the presence of Ti element than the case without Ti in the alloy according to the microstructure analysis of the Al-Si casting and forging alloy. Primary Al3(Sc,Ti) particles can formed in the as-cast alloy, and are good heterogeneous nucleus in the process of alloy solidification. In addition, the secondary Al3(Sc,Ti) particles are precipitated out in the form of dispersion in the alloy after aging treatment, and play an important role for precipitation strengthen. The comprehensive mechanics performance are improved caused by adding Sc.