Rheo squeeze casting of aluminum alloy

The semi-solid slurry of high strength wrought aluminum alloy 7075 was prepared by lspsf process. The rheo indirect squeeze casting was carried out on the model j15-300 vertical semi-solid squeeze casting machine developed in the laboratory. The rheo indirect squeeze casting of small batch wheel shaped parts was successfully realized. The process parameters of squeeze casting equipment were set and adjusted. The effects of different extrusion pressure on the properties of the parts were investigated. The microstructure characteristics and defects of the wheel shaped parts in rheo squeeze casting were described. The mechanical properties of the parts in as cast state, heat treatment state and tensile fracture characteristics were analyzed

(1) Continuous and high quality 7075 semi-solid slurry can be obtained by lspsf process, which can meet the mass production of 2kg parts. When the pouring temperature is 630 ~ 636 ℃, the mold temperature is about 200 ℃, the holding time is 15s and the specific pressure is 80MPa, the blank of 7075 aluminum alloy wheel parts is formed by rheo squeeze casting. The appearance quality is good, and there are no cracks, pores and shrinkage porosity. The microstructure grain is fine and non dendritic.

(2) The results show that the mechanical properties of rheo squeeze casting are better than that of conventional casting. The average tensile strength is 299mpa, the average elongation is 15.32%, and the maximum elongation after fracture is more than 23%.

(3) Because of the lower pouring temperature and less heat, the microsegregation in the microstructure of 7075 alloy rheo squeeze casting is smaller than that of conventional liquid squeeze casting.

(4) After T6 heat treatment, the mechanical properties of 7075 alloy by rheo squeeze casting are greatly improved. The average tensile strength is 520mpa, the average yield strength is 467mpa, and the average elongation is 9.05%. The maximum tensile strength is 552mpa, the maximum yield strength is 500MPa, and the maximum elongation is 13.77%. The best performance index reaches the forging level.

(5) With the increase of injection specific pressure, the tensile strength increases, but the plasticity does not increase after a certain increase. Under the experimental conditions, when the injection specific pressure is 80 MPa, excellent parts can be produced.

(6) The larger the injection pressure is, the finer the grain is. The results show that the liquid phase segregation occurs in the direction of free surface in the cross section of wheel shaped parts in rheo squeeze casting. The larger the pressure gradient is, the more spherulites there are and the greater the degree of segregation is.