Research On Solidification Microstructure And Mechanical Properties Of Al-18Si Alloy

Hypereutectic Al Si alloy has high specific strength,high thermal stability,good wear and corrosion resistance and excellent casting properties.Therefore,it is widely used in automobile,aviation and other processing and manufacturing industries.The coarse primary silicon in hypereutectic Al Si alloy seriously splits the continuity of the matrix.Under the action of applied load,it leads to stress concentration,which leads to the obvious reduction of the mechanical properties of hypereutectic Al Si alloy.Therefore,how to refine the size of primary silicon in the solidification structure of the alloy through a simple melting process is an effective method to improve the mechanical properties of hypereutectic Al Si alloy.Therefore,the research on solidification structure and mechanical properties of Al-18 Si alloy has very important industrial application value,which can further expand the application of Al-18 Si alloy in industrial production.In this paper,the effects of different melting and casting processes on the solidification structure and mechanical properties of Al-18 Si alloy were studied by means of optical microscope,scanning electron microscope,energy dispersive spectrometer and electronic universal tensile testing machine.The following research results were obtained:The effect of liquidus casting on the solidification microstructure and mechanical properties of Al-18 Si alloy was studied.The results show that co MPared with the traditional melting method,liquidus casting has an obvious refining effect on the primary silicon in the solidification microstructure of Al-18 Si hypereutectic Al Si alloy.With the increase of mold temperature,the size of primary silicon in Al-18 Si hypereutectic Al Si alloy increases,and the mechanical properties of the alloy also decrease.With the increase of holding time at liquidus temperature,the size of primary silicon in Al-18 Si hypereutectic Al Si alloy first decreases and then increases,and the mechanical properties first increase and then decrease.When the melt with liquidus temperature holding for 10 min is poured into the room temperature metal mold,the size of primary silicon in the solidification structure of Al-18 Si alloy is the smallest.The average size of primary silicon is 13.4 μ m.Maximum size 23.8 μ m.The tensile strength of the alloy reaches the maximum value of 212 MPa and the maximum elongation is 8.3%.The effect of melt pre precipitation on the solidification microstructure and mechanical properties of Al-18 Si alloy was studied.The results show that the melt pre precipitation at appropriate temperature can eliminate the primary silicon in the alloy structure.With the increase of melt pre precipitation temperature,the primary silicon in the alloy solidification structure α-The area fraction of Al first decreases and then increases.When the pre precipitation temperature is 635 ℃,α-The minimum al area fraction is 32.3%.When the pre precipitation temperature is 635 ℃,there is no primary silicon in the alloy structure.With the extension of melt pre precipitation time,the microstructure of the alloy increases α-The area fraction of Al first decreases and then increases.When the pre precipitation time is 10 min,α-The minimum al area fraction is 32.3%.When the pre precipitation temperature is 635 ℃,the room temperature tensile strength and elongation of Al-18 Si alloy increase first and then decrease with the extension of melt pre precipitation.When the melt pre precipitation time is 10 min,the maximum tensile strength of the alloy is 224 MPa and the maximum elongation is 10.3%.The results show that the effect of high temperature mixing temperature on the solidification properties of Al-18 Si alloy melt disappears with the increase of low temperature mixing temperature.When the high temperature melt is 830 ℃ and the melt standing time is 10 min,the precipitation of primary silicon in the alloy solidification structure changes obviously with the increase of the mass ratio of high temperature melt to low temperature melt.When the mass ratio exceeds 1:1,the primary silicon in the alloy solidification structure disappears completely;With the increase of high and low temperature melt mass ratio,α-The area fraction of Al first decreases and then increases.When the high temperature melt temperature is 830 ℃ and the high and low temperature melt mass ratio is1:1,with the increase of melt standing time,the size of primary silicon,the area fraction of primary silicon and α-The area fraction of Al first decreases and then increases.When the standing time is 10 min,there is no primary silicon in the solidification structure of the alloy,and α-Al area fraction reaches the minimum value of 37.1%.With the increase of the standing time of the mixed melt,the tensile strength and elongation of the alloy increase first and then decrease.When the standing time of the mixed melt is 10 min,the maximum tensile strength of the alloy is 221 MPa and the maximum elongation is 8.1%.