Although rheo squeeze casting can improve and improve the mechanical properties of 7075 alloy parts and eliminate some macro segregation, the micro segregation is still widespread, which reduces the grain boundary strength and leads to the low overall properties of rheo squeeze. 7075 alloy is a kind of alloy that can be strengthened by heat treatment, and its comprehensive mechanical properties can be improved by proper heat treatment process. According to the preliminary verification, the quality of 7075 alloy parts is good under the process conditions of specific pressure of 80MPa, mold filling speed of 0.2m/s, mold preheating temperature of 200 ℃ and pouring temperature of 635 ℃. The successful parts of rheo squeeze casting under the condition of the process parameters were selected, and the mechanical processing and wire cutting sampling were carried out according to figure 1. After sampling, T6 heat treatment was carried out according to the heat treatment process obtained from the experiment. Solution treatment at 475 ℃, 2 h, water quenching, and artificial aging at 160 ℃ for 16 h.
T6 heat treatment can greatly improve the mechanical properties of 7075 rheo squeeze casting alloy parts, the average tensile strength is 520mpa, the average yield strength is 467mpa, the average elongation is 9.05%, the maximum tensile strength is 552mpa, the maximum yield strength is 500MPa, the maximum elongation is 13.77%. Forming 7075 by rheo squeeze casting The alloy has certain advantages, from the elongation and tensile strength point of view, its single maximum value is at a good level, higher than the forging and national extrusion bar standard, the average value has declined, mainly due to the stability problem, the follow-up will be analyzed, how to improve the process, optimize the relevant parameters to improve the consistency of product performance, will be the focus of follow-up research.
The A1 sample with the best elongation and the F1 sample with the worst elongation were selected for SEM scanning and EDS analysis (see Fig. 2 ~ 6). It was found that there were certain inclusions on the fracture surface, which made the mechanical properties unstable. As a result, the rheo squeezewas applied to the actual production. There was also a key problem of how to avoid inclusions in the rheo squeeze casting process.