The Effects Of Remelting On Microstructures And Mechanical Properties Of Hypoeutectic Al-Si Alloy

Research the effects of partial remelting A357 alloy on microstructure and mechanical properties we refined and modified the alloy which containing retures in the sand casting process to fine the way to improve the alloy's properties.To use 4% Al-5Ti-1B intermediate alloy as refiner and 0.4% Al-10Sr intermediate alloy as modificator refined and modified on 730℃to research the alteration of microstructure and mechanical properties of the A357 alloys with 20%,30%,40% returns that the alloy was refined and modified on the same technology .The results show that comparing to the A357 alloy which didn't contain returns, the grain sizes of the alloy containing returns are smaller and its tensile strength and yield strength increase. Specially, the alloy containing 30% returns whose tensile strength increment rate is 20%, yield strength increase to 112MPa from 101MPa, and elongation increase by 39%.Al-10Sr intermediate alloy is a good modificator, it has a high quality ever to the alloy that contain returns. A357 alloy containing 30% returns was modified, the tensile strength and yield strength are the largest and its crystal grain size is the smallest, the alloy's elongation is the largest too, the area proportion ofα-Al dendrite is the smallest。Comparing to the new one's, its tensile strength increment rate is 8.4% and yield strength increase by 23.7MPa, elongation increase to 3.8% from 3.4%.After refined and modified, the majority shape of morphology of the eutectic Si is spotted but, when the percentage composition of returns is over 30%, there are a little flake shape eutectic Si. Comparing to the A357 alloy which didn't contain returns, the grain sizes of the alloy containing returns are smaller and its tensile strength and yield strength are the larger, as the A357 alloy containing 30% returns was refined and modified, its tensile strength increment rate is 9%, its elongation is from 2.1% to 3.9%.