Rheo-squeeze Casting Of A357 Alloy By Vibrating Sloping Plate Process

This paper based on the research and development of semi-solid rheo-forming technology at home and abroad,A357 alloy was selected as study object,effects of process conditions on the microstructure of A357 semi-solid alloy were studied.In addition,combined vibration sloping plate with squeeze casting for semi-solid rheological squeeze casting,effects of rheo-squeeze casting and heat treatment process conditions on the microstructure and properties of A357 alloy were studied.Main work and results are described as follows:(1)Effects of process conditions on the microstructure of A357 alloy semi-solid slurry were obtained:?Not only good microstructure of A357 alloy semi-solid slurry can be prepared but also can be flowed from the sloping plate of cuprum material with TiO2 coating;?Fine microstructure of semi-solid slurry can be prepared by the sloping plate with the shape of U,but sometimes molten alloy cannot flow from it,so straight sloping plate was chosen;?When casting temperature is between 640??720?,with the decrease of casting temperature fine microstructure of semi-solid slurry could be prepared.When casting temperature was at 640?,crust was produced;?When vibration frequency is between OHZ?100HZ,with the increase of vibration frequency,the grain size and roundness first decrease and then increase;?When sloping plate length is between 100mm?550mm,with the increase of sloping plate length the grain size and roundness decrease;? Under the current experimental conditions,the straight sloping plate is designed by cuprum with Ti02 coating,pouring temperature is 660?,the vibrating frequency is 60Hz,the plate length is 550mm,fine non-dendrite microstructure of A357 were obtained by vibrating sloping plate process.At the same time,alloy solution could flow from the sloping plate.(2)Combined vibration sloping plate with squeeze casting,producing the A357 alloy casting part successfully,effects of vibration sloping plate and casting temperature on the formability?microstructure and property of A357 alloy casting part were obtained.When casting temperature is 690? and 700?,alloy casting was filled completely;When casting temperature is 670? and 680?,alloy casting was not filled completely,at the same time,cold-separation and shrinkage were also existed in the alloy casting part.With the decrease of casting temperature,fine and spherical microstructure of A357 alloy semi-solid rheo-squeeze casting part could be prepared.When casting temperature is 690? of semi-solid rheo-squeeze casting.the mechanical properties of A357 alloy is the best,tensile strength is 231.7±3.5 MPa,elongation is 6.8±0.1%.Compared with liquid squeeze casting part,tensile strength is 207.5 MPa±2.4 MPa,elongation is 5.6±0.1%.mechanical properties were improved 11.7%and 21.4%respectively.(3)Heat treatment for the A357 alloy casting part,effects of heat treatment technology on the microstructure and property of A357 alloy semi-solid rheo-squeeze casting part were obtained.Solution temperature is at 540?,with the increase of solution time,tensile strength,elongation and Vickers-hardness increase firstly,then become thick;When solution time is 6h,mechanical property is the best.After solution treatment for 6h,then aging,with the increase of aging time,tensile strength and elongation firstly increase and then decrease,but elongation decrease all along;When the aging time is 4h,tensile strength is maximum of 345±6.9MPa,elongation is 7±0.2%;optimal heat treatment process is solution for 6h and aging for 4h.Compared with liquid squeeze casting part after T6 heat treatment of 330.5±6.6MPa and 5.6±0.17%,mechanical properties were improved 15MPa and 1.4%respectively.