Study On Extrusion Process,microstructure And Properties Of High Quality Aluminum Strontium Alloy

Al-Si alloy has excellent properties of casting,corrosion resistance and heat resistance,thus has been widely used in the automotive and aerospace industries.During the casting process of Al-Si alloy,it is easy to form coarse eutectic Si,which seriously deteriorates the mechanical properties and processing performance of Al-Si-based alloys.In order to solve this problem,the Al-Si alloys need to be modified during the production process.Al-10Sr alloy is often used as a modifier of as-cast Al-Si alloys due to its advantages of long effective modification time,no excessive modification,and no pollution to the environment.The modification performance of the Al-Sr alloy depends on the morphology and the size of Al₄Sr phase.This article takes the Al-10Sr alloy as research object,in this paper,the hot compression experiments were carried out on the Gleeble-3500 thermo-mechanical simulator to study the hot flow stress and microstructure evolution of Al-10Sr alloys.And then based on the results of hot deformation and processing map analysis to select the best processing parameters to carry out horizontal extrusion and repetitive continuous extrusion experiments,and use finite element analysis technology to analyze those two extrusion processes.Finally,the modification performance of the Al-10Sr alloy after horizontal extrusion and continuous extrusion was measured.The main results of this paper are as follows:(1)The true stress-strain curve of Al-10Sr alloy showed slight flow softening characteristics.The peak stress decreased with the increase of temperature and the decrease of strain rate.The flow stress of Al-10Sr alloy can be described by the constitutive equation with the deformation activation energy of 222.23k J/mol.During hot compression testing,plastic deformation mainly occurred in soft Al matrix and Al4Sr phases were slightly broken.With increased deformation temperature and decreased strain rate,the size of Al₄Sr phases gradually increased.(2)Based on the dynamic material model,the processing maps of Al-10Sr alloy under different strain conditions were established.The results showed that as the strain increases,the area of the instability zone first decreases and then increases.When the strain is 0.5,the area of the instability zone is the smallest,and the optimum processing parameters were the temperature of 460-530 ^oC and the strain rate of 0.2-1s^-1.The microstructure corresponding to the processing maps showed that the Al matrix defects in the safe zone were significantly smaller than the instability zone,which verified the accuracy of the processing map.(3)Both horizontal extrusion and continuous extrusion can effectively eliminate the defects in the as-cast Al-10Sr alloy,and significantly refine the size of the Al₄Sr phases.Compared with horizontal extrusion,the Al₄Sr phases processed by continuous extrusion were more significant refined.After three continuous passes,the average length and width of the Al₄Sr phases were 11 and 8.3?m,respectively.Numerical simulation of these two extrusion processes of Al-10Sr alloy showed that compared with horizontal extrusion,there are a severe shear band in the continuous extrusion process,and the temperature field changes from room temperature to extrusion temperature,these features make continuous extrusion have a better refinement effect.(4)Compared with as-cast Al-10Sr alloy,horizontal extrusion and continuous extrusion Al-10Sr alloy had better modification effect on 4343 aluminum alloy,and continuous extrusion Al-10Sr alloy had the best modification effect.Most of the eutectic silicon in the 4343 aluminum alloy after continuous extrusion of the Al-10Sr alloy is in the form of fine particles,with an average size of about 13.7?m.