The equipment of rheo squeeze casting is few, and the general experiment is to use the general four column hydraulic press or the horizontal hydraulic forging machine modified by the die casting machine. The experimental equipment adopts the specially designed and developed model j15-300 vertical squeeze casting molding machine, which adopts the structural system of vertical clamping and clamping, horizontal feeding of bottom barrel, bottom up injection casting and vertical secondary pressure molding. The closing force is 3000kN, the injection force (maximum) is 940kn, and the inner spacing of the table rod is 620 × 620mm. The process parameters of rheo squeeze casting include: quality of liquid metal, pouring temperature of slurry (mainly controlling solid phase ratio of slurry), punching speed, pouring temperature, preheating temperature of die, specific pressure, holding time of squeeze casting, etc. Due to the lack of research on rheo squeeze casting, according to the process of liquid metal squeeze casting, thixoforging and a small part of rheo squeeze casting, the selected process parameters are as follows:
① The results show that the casting temperature of 7075 alloy is 680 ~ 700 ℃ in full liquid state and 628 ℃, 630 ℃ and 635 ℃ in semi-solid slurry;
② The filling speed is 0.1 ~ 0.3m/s;
③ The preheating temperature of die (punch and die) is 200 ℃;
④ The holding time of squeeze casting is 15s;
⑤ The specific pressure is 70MPa, 80MPa and 90Mpa;
⑥ Mold lubricant is coating lubricant.
The selection of heat treatment parameters for successful parts: according to the heat treatment specification of 7075 alloy, several samples were selected for heat treatment process test. After test verification and analysis, the heat treatment parameters for 7075 rheo squeezewere selected as follows: solution treatment temperature 475 ℃, holding temperature 2h, water quenching; T6 artificial aging temperature 140 ℃, holding temperature 16h, air cooling.
Samples of 10 × 10 × 10 mm are processed in different positions in the middle of the successful parts, and then inlaid into metallographic samples, and marked on the sample bag. The samples were coarsely ground and finely ground with 320#, 600#, 800#, 1200#, 1500# SiC water abrasive paper, and then polished with metallographic polishing machine with a size of 2.5 m m diamond abrasive spray or alumina solution. Finally, the mixture was mixed with Keller reagent and 2mlHF+3mlHCl+5mlHNO3+230mlH2O mixed acid water to corrode, then 15~25s at room temperature.
The metallographic structure was observed and photographed by aixio scope A1 optical microscope system in the laboratory, and measured and analyzed by IPP and related software. The phase composition and morphology were analyzed by SEM secondary electron imaging and energy spectrum analysis, and the phase composition was determined by XRD. The standard tensile specimen with round bar shape was made by wire cutting and turning in the middle of the as cast and heat-treated parts. The mechanical properties of wheel like parts were analyzed on css-44200 electronic universal testing machine.