Investigation On Hot Deformation Mechanisms And Spinning Forming Process Of A356Casting Alloy

As a kind of Al-Si-Mg series alloy, the A356alloy plays an important role in light weight materials for automotive and is widely used for body, wheel and other important car parts, because of its good cast ability, high mechanical properties and many other advantages. Currently, the aluminum alloy wheels which are mainly produced by low-pressure die casting technology can not meet the large size and high load demand. And the aluminum wheels produced by forged technology are limited by their higher costs. The aluminum alloy wheels produced by spinning which have the advantages of unconstraint of sizes, beautiful appearance, good performance, high security, saving materials, etc has become a new forming technology and has a good momentum of development. By combining the advantages of low cost of castings and high quality of forged wheels,"the new spin-cast process," which means hot spinning is used to cast billets, has become a significant development of manufacturing technology of aluminum alloy wheels. However, the basic research on hot spinning technology for cast aluminum alloy is still limited. Therefore, deformation mechanism and process optimization for the hot spinning process of casting A356aluminum alloy will be systemically studied in this paper.First, the hot deformation behavior and mechanism of the A356alloy were studied by hot compression test and tensile test. True stress-strain curve at different deformation temperatures and strain rates were obtained, and the effect of deformation conditions on flow stress was studied. The results showed that the flow stress is more sensitive to deformation temperature than strain rate. Through high temperature deformation kinetics analysis and microstructure observation, the hot compression deformation mechanism of the cast A356alloy is determined to be dynamic recovery. And the constitutive equation of A356alloy during hot defomiation was established. Then the hot spin ability of A356alloy was studied by high temperature tensile plasticity and hot processing map analysis. The appropriate spinning forming conditions for A356alloy were determined to be:temperature330℃～360℃, strain rate10s-1～50s-1. On the basis of above research, hot spinning experiments of A356alloy wheels were carried out and the effect of hot spin deformation on microstructure and mechanical properties of A356alloy were analyzed. As the deformation degree increases, the tensile strength increases gradually and the elongation was significantly improved, especially when the spinning deformation degree exceeded30%. The microstructure observation showed with the deformation increases, the initial cast dendrite structure changed into band structure with reduced dendrite arm spacing and eutectic silicon particle were broken and refined. The longitudinal flowing lines observation showed non-uniform deformation across the wall thickness with less deformation in the center outside surface.Then three-dimensional finite element model for hot spinning process of A356alloy wheels was established, and the effect of spin wheel structure and open angle of wheel perform on the strain distribution was simulated, and finally optimized spin wheel structure and open angle of wheel perform were verified by experiments to improve the deformation uniformity.