Study On Microstructure And Properties Of High Yield Strength Aluminum Alloy

Aluminum alloy is used for shipbuilding for hundreds of years.With the development of shipbuilding industry,increasingly importance has been attached to light-weighting of ship.Yield strength and corrosion-resistance requirements of materials for shipbuilding are getting higher and higher.A357 alloy has a good performance in casting,anti-fatigue,corrosion-resistance and airtightness.It has been used widely in the aviation industry and the automotive industry.And it is of great practical value to improve its yield strength without reducing the corrosion resistance through optimizing the composition and process of A357 alloy.In this paper,the effects of Si,Cu,Mg and Mn on the mechanical properties and corrosion-resistance of metal mold casting Al-Si alloy were studied.The orthogonal experiment with four factors and three levels was designed to determine the optimal composition of the alloy.The modification effects of optimal composition alloy with different Sr concentration were analyzed.The aging process of the new alloy was optimized.The microstructure of the alloy was observed by SEM.The fracture morphology of the alloy was observed and the fracture mechanism was analyzed.The corrosion-resistance of the new alloy and A357 alloy was compared.The results show that with the increase of the concentration of Si,Mg and Cu,the yield strength of the alloy increases.With the increase of Si concentration,the elongation of the alloy decreases and corrosion resistance is first slightly weakened and then enhanced.With the increase of Cu concentration,the corrosion resistance is obviously weakened.The optimized composition is Si: 8.3 wt.%,Cu: 0.1 wt.%,Mg: 1.0 wt.%,Mn: 0.1 wt.%.0.06 wt.% Sr has good modification and refinement effects on the silicon in the new alloy.The silicon phase is distributed in the matrix after the heat treatment and the particle size is about 5?m.The manganese-rich phase is in the form of fine particles.Cu and Mg are mainly distributed in the matrix in the form of dispersed desorption phase.The elements of hypermetamorphic aluminum alloy are enriched in grain boundary and the plasticity of alloy is poor.When the aging temperature is 170 ?,the aging time of 8 hours can get the desired yield strength and elongation.The yield strength of the new alloy is 322.5MPa.The elongation of the new alloy is 3.2% and the corrosion resistance of the new alloy is better than that of A357 aluminum alloy.The alloy with different content exhibits ductile fracture with dimples.The effects of silicon content on fracture morphology are significant.With the increase of silicon content,the dimple area gradually becomes smaller and the depth gradually becomes lighter.The amount of brittle phase in the matrix and the tear edge also gradually increased with plasticity decreased.