Research On Microstructure And Defects Characterization And Their Effects On Mechanical Properties Of Al-10Si-0.3Mg Alloy Thin-wall Die Castings

Due to its high production efficiency,high casting precision,good performance and simple manufacturing process,die casting technology is a widely used process.Die casting Ai-Si alloys are widely used in automotive structural parts,especially large-sized thin-walled parts with complex shapes because of their excellent fluidity and filling ability,good corrosion resistance,high strength and dimensional accuracy.However,for the die casting process,because of its fast filling speed,it is easy to cause air entrainment and form pores.Even with vacuum die-casting technology,it is difficult to avoid the formation of pores in the alloys,and these pores have a significant influence on the mechanical properties of alloys.The research on the three-dimensional representation of pores and its influence on deformation behavior is one of the research hotspots and difficulties in this field.This paper has discussed about the research on microstructure and pores characterization and their effects on mechanical properties of Al-10Si-0.3Mg Alloy thin-wall die castings.The microstructure of the alloy was characterized before and after heat treatment,and the hardness test and tensile test were carried out to analyze the effect of heat treatment on the mechanical properties.The X-ray computed tomography(CT)technique was used to quantitatively analyze the morphology and characteristics of the pores.And combined with Digital Image Correlation(DIC)technology and tensile experiments,the effects of pores on mechanical properties and deformation behavior were analyzed.The main conclusions are summarized as follows:① The microstructure of Al-10Si-0.3Mg alloy is mainly composed of aluminum matrix,eutectic Si structure and AlSiFeMn phase.The aluminum matrix exhibits a distinct gradient distribution along the thickness direction.After heat treatment,the eutectic Si structure is composed of continuous coral transformation into a spherical shape;②In the as-cast condition,the hardness of the sample shows a gradient distribution along the thickness direction.After the heat treatment,the hardness decreases significantly and the gradient disappears.The yield strength and tensile strength decrease,and the elongation increases remarkably.③ The local porosity at the fracture region is closely related to the elongation of the metal,but it is difficult to accurately predict the fracture location.It can be determined that the local porosity is the main factor affecting the fracture location.When the sample has large pores(volume≥0.06 m3),the fracture location is also related to the largest pore;④The highest local porosity in the sample has a significant linear relationship with the elongation of the sample:the samples only with low porosity(highest local porosity ≤1.0%)exhibit good ductility(ε≥12%);the samples with medium local porosity(1.0%～1.6%)exhibit acceptable ductility(7%≤ε≤12%);the samples with high porosity(>1.6%)exhibit poor ductility(ε≤7%).