Semi-solid Hypereutectic Al-si Alloy Rheological Squeeze Cast Piston Technology Research

The semi-solid rheocasting is a hot research subject in the domestic and international academe of SSM presently. The Semi-solid squeeze casting is a new technology to product the piston which is combined on the basis of the semi-solid rheocasting and the squeeze casting. It has a prominent merit of short production flow, high availability ratio of material, low energy and so on . The paper systematically has conducted the interrelated basic research of craft, and select the ZL117 alloy piston to come to substitute the ordinary eutectic Al-Si alloy piston which was produce by metal mould, It has vital significance to the development of SSM and the exploiture of new piston. The paper makes a integrate technological parameter through the infection of all kinds of technological parameter to structure and mechanical properties of the casting.The paper designed and processed a piston mold for the semi-solid squeeze casting. Tests showed that the mold can product continuously and the piston has good appearance quality, compact structure and high mechanical properties.The paper research systemicly the influence of three technologies (specific pressure, dwell time and temperature of mold) to the structure and mechanical properties of the casting through one-factor test. The results show that the structure of the casting be more compact with improving the specific pressure, and the mechanical properties too. But when specific pressure reached to 140Mpa, mechanical properties improves unconspicuously. Along with the dwell time prolongs, mechanical properties of the casting was enhanced, when dwell time reached 75s, mechanical properties improves unconspicuously. Along with the temperature of mold improving, strength and hardness depresses, and plasticity increased. When the temperature exceed 150-170℃, mechanical properties improves unconspicuously. So for the semi-solid squeeze casting piston of ZL117 alloys, the best technology: specific pressure is 140Mpa,dwell time is 75s,the mold temperature is 150-170℃,clampingtime is 5-7s, squeeze velocity is 0.1m/s.Under the best technology parameters ,the mechanical properties is σb = 254.95MPa, δs = 0.484%, HBS=128.In the end, the paper analyzed the obdurability mechanism of semi-solid squeeze casting. Male die reinforces the flow of semi-solid slurry in the impression, wash out crystallizing layer, change the shape of arborescent crystal. Making the casting be pressed from various direction be propitious to pressure transmission, enhanced the feeding effect, which can decrease the shrinkage porosity of ZL117 alloys. Crystallization under the pressure can refine and change the structure, lighten the gravity segregation, improve the mechanical properties conspicuously. Semi-solid slurry has unique characteristic and alloying. The pressure prevent the gas liberation and formation of air bubble.