Study On The Superplastic Deformation Of Al-12.7Si-0.7Mg Alloy

The abrasion resistance is better and coefficient of linear expansion is lower with the increase of the content of silicon in Al-Si alloy. Its strength is high but plasticity is very low. It can be formed in small tonnage equipment, with the technology of superplastic deformation. Based on the reasons above, this paper studied on the superplastic deformation behavior of Al-12.7Si-0.7Mg alloy. The influence on high temperature flow stress and elongation at different temperature and strain rate conditions with high temperature tensile test was investigated.The deformation mechanism and the organization evolution law during the deformation was studied with optical microscope, SEM, TEM and some other analysis methods.The main results obtained as follows:1. Under the deformation condition of the temperature of460～520℃and the strain rate of1.67×10-4s-1～1.+67×10-3s-1, the flow stress of the Al-12.7Si-0.7Mg alloy increases with the increase of strain rate and the decrease of the temperature. And the elongation of the alloy decreases with the increase of strain rate and the decrease of the temperature. In some deformation conditions, when the strain reached a certain value, the flow stress increased again, strain hardening appears.2. The strain rate sensitivity index (respectively0.31-0.52) and deformation activation energy (149.18KJ/mol) of this alloy were got through calculations. It can be decreased that the atoms diffusion mechanism of Al-12.7Si-0.7Mg alloy is a compound mechanism which deformation is grain boundary sliding primarily accommodated by intragranular dislocation slip controlled by the diffusion.3. The grain size of the Al-12.7Si-0.7Mg alloy is close to10μm, with the equiaxial shape and the second phase round particles. During the superplastic deformation, the grain mainly deforms through sliding and rotation. There is slightly grows up of the grain during sliding and rotation and remain good equiaxial shape at the same time. The fracture surface of the samples after high temperature superplastic deformation contains a large amount of dimples. The fine equally distributed dimples shows that the fracture of the alloy is ductile one.4. Along with the sliding and turning of Al matrix during superplastic deformation, cavities appear at the interface of the two phases. With the growing of the cavities, the cavities near each other connect and develop to micro cracks which extend along the grain boundary. The cracks extend continuously and interlink, and lead to the fracture of the materials at last.