Abstract
Abstract Semisolid slurry of ZA27 alloy was prepared by Self-inoculation Method (SIM), the effects of isothermal holding parameters on microstructures of rheo-diecasting were researched, and the mechanical properties of ZA27 rheo-diecastings were tested. The results indicate that the dendritic microstructure of ZA27 alloy formed by permanent mold casting can be significantly modified by RDC with SIM, and obtain fine spherical microstructures. After comprehensive consideration, the suitable melt treatment temperature for the ZA27 alloy semisolid processing is 550~560°C. The isothermal holding process of ZA27 alloy slurry has great effect on primary α-Al particles (α1), while has little effect on the microstructure of secondary solidification in the process of thin-walled rheo-diecasting, and the suitable isothermal holding time of semisolid slurry for rheo-diecasting is 3 min. Compared with HPDC, the RDC process can increase the tensile strength of ZA27 alloy by more than 6.9%, with a maximum increase of about 12.5%. The best performance die casting can be obtained when the slurry holding time is 3-5 min.
Highlights
Zn-Al series alloy have wide range of uses in structural materials and wear-resistant sealing materials due to its excellent casting properties, high mechanical properties and wear resistance, good castability, good workability and low raw material costs[1], which is the ideal material to replace expensive copper alloy
It can be seen from the scheil solidification curve in Figure 3 that the solidification process starts when the temperature is about 490°C, and the eutectic reaction starts when the temperature is about 380°C, meaning that the liquid/solid temperature range of the ZA27 alloy is about 110°C, which is suitable for semisolid processing
It has been measured via the experiment that the average change of the melt temperature during the slurry preparation of the Self-inoculation Method (SIM) process is about 80°C, which means that the melt treatment temperature range can be controlled to 540°C~570°C
Summary
Zn-Al series alloy have wide range of uses in structural materials and wear-resistant sealing materials due to its excellent casting properties, high mechanical properties and wear resistance, good castability, good workability and low raw material costs[1], which is the ideal material to replace expensive copper alloy. High pressure die casting (HPDC) is a processing technology that applies high pressure to molten metal to form metal parts. The apparent viscosity of the semisolid slurry is higher than that of the liquid metal, its flow is more stable than the liquid state during the die-casting and filling stage, which can effectively reduce or even eliminate the injection, turbulence and gas phenomenon during liquid metal injection. The semisolid rheological die-casting (RDC) technology using semisolid slurry combined with HPDC can further improve the mechanical properties of the casting. Materials Research on microstructures and mechanical properties of ZA27 alloy were studied to provide a theoretic basis for the optimization of process parameters and its application
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