The Study On Technology Of Thixo-Diecasting Al-30Si Alloy

In this paper, Al-30Si as experimental materials was used. Al-30Si in the isothermal process of organizational evolution after modification with phosphate salt was studied, analysis of isothermal treatment on microstructure of Al-30Si, and to explore the mechanism of organizational evolution on isothermal process; also studied the isothermal heat treatment process and casting process parameters on the Al-30Si thixotropic semi-solid casting organizations and properties. As a comparison, also on Al-30Si liquid die casting corresponding research done.The results show that: primary silicon was smallest, most uniform distribution, the organization best of Al-30Si when the amount of phosphorus salt added to 1%; primary silicon is reduced from the original 200μm to an average of 26μm. test rod ofφ15mm heart and external organization changed little; primary silicon of trial bar ofφ75mm was increasing from the outside to the heart, the size of primary silicon was increased from 40μm to 50μm.In the process of isothermal treatment, low melting point eutectic organization in Al-30Si first began to melt with the holding temperature or holding time; penetrate liquid connect with a continuous network each other,αphase in which to form a spherical or nearly sphericalαphase will be surrounded by the eutectic. Additional holding time, size of sphericalαphase decreases until it disappears;α-phase around the primary silicon nucleation and growth, can formed a sunflower-like organization after the water quenched. Primary silicon in the process of isothermal was melt,the size decreases then combined grew up, and gradually the whole of the circle with increased holding time. After water quenched, Al-30Si Brinell hardness and wear resistance has gteatly improved compared with the cast.The size of primary silicon in Al-30Si liquid die casting organization is constantly decreasing with the pouring temperature, it has been a significant decrease occurred when the temperature increases from 780℃to 820℃, then the changes at elevated temperatures not obvious. Trend of tensile strength with temperature has the opposite trend of the primary silicon size; Brinell hardness increased with pouring temperature did not show obvious rule, but overall is reduced. Effect of injection speed was much smaller than pouring temperature on the Al-30Si liquid die-casting organizations. Tensile strength and Brinell hardness emerged increase and then decrease with the increase of injection speed. Semi-solid thixotropic compared with Casting organizations, the morphology of primary silicon is more round, needle-like eutectic silicon was disappeared, whileα-Al dendrites were broken in order to diffuse granular distribution; The form ofα-phase was spherical or nearly spherical shape when solid fraction is high,. Tensile strength with the increase of injection speed shows the trend of first increase and then decrease at 620℃incubated 100 min and 120 min, incubated at 630℃120 min, the tensile strength with the increase of injection speed gradually reduced at 630℃incubated 120 min. Brinell hardness increased with increasing holding time or holding temperature decreases; with injection speed first increases and then decreases.