Effects Of Micro-alloying And Hot Rolling On Microstructure And Mechanical Properties Of Al-Si-Mg Based Aluminum Profile

Near eutectic Al-Si-Mg alloy has many advantages, such as excellent castability, high mechanical properties and low cost, compared with traditional 6xxx aluminum alloys. Previous studies of our group show that near eutectic Al-Si-Mg alloy has excellent formability of hot deformation, and possesses a good combination of tensile strength and elongation by hot deformation. Thus, it has a powerful potential to replace 6xxx aluminum alloys for manufacturing aluminum profiles. The main aims of this paper are as follows:based on near eutectic Al-Si-Mg alloy, to develop a technology combined micro-alloying and hot rolling to manufacture aluminum profiles with a high performance and low cost, to investigate effects of the micro-alloying by Zr, Ti and V and processing parameters of hot rolling on microstructure and mechanical properties of the near eutetic Al-Si-Mg alloy.Micro-alloying by Zr, Ti and V has no considerable influence on the microstructure and mechanical properties of both the as-cast and as homogenized specimens, but leads to a considerable increase in the yield stength, ultimate tensile stength and elongation to fracture of the as-rolled specimens. It is found that the micro-alloying has a great influence on the microstructure evolution during hot rolling. On the one hand, it suppresses the progress of dynamic recrystallization, on the other hand, it also restrains the dynamic precipitation of Mg2Si phase. The combined impacts of the micro-alloying to dynamic recrystallizing and precipitating are thought to be responsible for the considerable improvement of the as-rolled mechanical properties. Result also reveals that the ability of restraining dynamic precipitation by V or Zr is stronger than that by Ti.The temperature and reduction ratio of hot rolling have an obvious impact to the microstructure and mechanical properties of the near eutectic Al-12.5wt%Si-0.6wt%Mg-0.1wt%Ti profile. It is found that either decreasing the rolling temperature or increasing the reduction ratio enhances the dynamic precipitation of Mg2Si phase. These dynamic precipitation particles have no strengthening effect on the matrix, conversely weakening the solution strengthening, however, they can pin the crystal boundary migration and result in grain refinement of recrystallization. In the case with a 33% reduction ratio, increasing the rolling temperature from 500℃ to 540℃, the yield strength and ultimate tensile strength are improved by 12% and 20% respectively, mainly related to the suppression on dynamic precipitation of Mg2Si phase induced by temperature effect. In the case at a hot temperature of 540℃, the yield strength, ultimate tensile strength and elongation to fracture are increased with the reduction ratio, and the much finer recrystallization structure is thought to be responsible for it.Combined micro-alloying with hot rolling, the Al-12.5wt%Si-0.6wt%Mg-0.1wt%Ti alloy has a good combination of strength and elongation, of which the as-rolled yield strength, ultimate tensile strength and elongation to fracture are 173.3MPa,243.8MPa and 9.4% respectively. And the proper hot rolling process for this alloy is obtained as:rolling at 540℃ with a reduction ratio of 67%.