Study On The Preparation Process And Modification Of The Efficient Al-Sr Master Alloy

Al-Si alloy is widely used in the aviation, aerospace, automotive, machinery and other fields because of its low density, high strength, good casting properties and corrosion resistance, low coefficient of thermal expansion and so on. Sr is the common modifier for Al-Si alloy and has a good modification effect. The element of Sr exists in the form of Al4Sr phase in the microstructure of Al-10% Sr master alloy, the mechanical properties and modification effect of Al-Sr master alloy are decided by the grain size and the morpholoty of Al4Sr phase. This article on Al-10% Sr master alloy as the research object, the effect of mechanical properties, microstructure and its impact modification of Al-Sr master alloy by squeeze casting billet after hot extrusion and ultrasonic melt treatment billet after hot extrusion is discussed. The effect of ultrasonic melt treatment time and frequency on mechanical properties, microstructure and its impact modification of Al-Sr master alloy are investigated in this article.The results showed that Al-Sr master alloy formed by gravity casting billet after hot extrusion, and the elongation of is 19.17%, respectively. The Al4Sr phase is massive and coarse and the mean radius of it is 68.3um. The Al4Sr phase in the microstructure of Al-Sr master alloy formed by squeeze casting billet after hot extrusion is refined obviously and a mean radius of 25.4um, an elongation of 24.74% is obtained. the size of Al4Sr phase is more small and dispersed evenly in the alloy formed by ultrasonic melt treatment billet after hot extrusion. The mean radius of it is 20.3um, and the elongation is 25.12%.Al-Sr master alloy formed by gravity casting billet after hot extrusion has a longer incubation period of metamorphic. The best modification effect occur on around 20 min. Al-Sr master alloy by squeeze casting billet after hot extrusion and ultrasonic melt treatment billet after hot extrusion have shorter incubation period of metamorphic and the best modification effect on around 5 min. the effect of modification Al-Sr master alloy by ultrasonic (?)atment billet after hot extrusion is also good on around 60min.The best time of ultrasonic melt treatment was 30s, and the elongation of Al-Sr master alloy is 8.12%, respectively. The microstructure of Al-Sr master alloy is improved remarkably. The Al4Sr phase is more smaller and dispersed, its length is between 60-560um and the width is between 20-70um. The best modification time of the Al-Sr master alloy formed by ultrasonic melt treatment of 30s on 20min.The best ultrasonic melt treatment frequency of Al-Sr master alloy formed by ultrasonic melt treatment billet after hot extrusion is 22kHZ and then the tensile strength is 26.73% The solution treatment eliminate the residual stress of Al-Sr master alloy generated during hot extrusion and the tensile strength and elongation of alloy after solution treatment is 27.21%, respectively. The Al4Sr in the micro structure of Al-Sr master alloy formed by the frequency of 22kHZ is small and dispersed evenly and its equivalent circle radius is 18.4um. Sr metamorphic changed the growth pattern of the eutectic silicon from needle-like to small coral-like and increase the eutectic silicon branches. The Al-Sr master alloy formed by the frequency of 22kHZ has the shortest incubation period of metamorphic, and the good eutectic silicon tissue is obtained on around 2min. the Al-Sr master alloy formed by three kinds of ultrasonic frequency all have better modification effect on around 60 min.