Effect Of Cu/Er Elements And Heat Treatment On Low Temperature Properties Of Casting Al-Si Alloy

Al-Si casting alloy has the advantages of good castability and high airtightness,and its application fields are extremely wide.Among them,the most representative is the Al-Si alloy material for high-speed train corbels.At this stage,our country has just broken through the barrier that all relevant technologies for corbels of high-speed EMUs rely on imports.However,there are few studies on the complex temperature environment of China plateau areas and the north and south.Therefore,the performance research of Al-Si alloy materials in low temperature environments is of strategic and forward-looking meaning.This subject adopts the metal mold casting process to prepare Al-Si alloys.By adding rare earth Er elements,Cu elements and Cu-Er composite elements to the casting Al-Si alloys,the overall performance of the alloys under low temperature environments is improved,and the composition is optimized.The Al-Si alloy undergoes subsequent heat treatment to further improve the microstructure of the alloy,enhance the strength and toughness of the alloy,and study the effect of heat treatment on the low temperature performance of the Al-Si alloy.The results show that after adding rare earth Er element,Cu element and Cu-Er composite element to Al-10Si-0.3Mg base alloy.The strength of the three groups of alloys with different compositions has been improved at room temperature(20?).But after adding Cu element and Cu-Er composite element,the elongation of the two groups of alloys both decreased.Stretching at-60?,the influence of alloying elements on the tensile properties of Al-Si alloys is consistent with that of stretching at 20?,and the low temperature tensile strength is higher than room temperature,but the elongation is reduced.After adding Cu element to Al-10Si-0.3Mg alloy,short rod-like Al₂Cu phase and grid-like Al-Si-Cu-Mg quaternary phase appeared in the alloy,alloy elongation is significantly reduced.The addition of rare earth Er elements can refine the Si phase grains of Al-Si alloys and increase the number of slip bands near the tensile fracture.After adding Cu-Er composite elements,the number of fractured second phases near the tensile fracture of Al-Si alloys is obvious reduced,the tendency of crack propagation and connection is extremely insignificant.Stretching at-60?,the influence of the addition of alloying elements on the number and morphology of the slip zone near the fracture of Al-10Si-0.3Mg alloy is consistent with the stretching at 20?,but the quantity is smaller and the morphology is more shallow.The best solution time of Al-10Si-0.3Mg alloy is 6h.At this time,the Si phase in the alloy is highly rounded,which reduces its splitting effect on the?-Al matrix,and the alloy's tensile properties has been improved in low temperature environments.Under the same heat treatment conditions,the tensile strength at-60°C is higher than room temperature,but the elongation is opposite.After the Al-10Si-3Cu-0.3Mg alloy is solid-solved for 6 hours,the tensile strength and yield strength of the alloy are significantly increased,but the elongation rate is decreased.After Al-10Si-0.3Mg-0.2Er alloy is treated with T6,the Si phase in the alloy becomes granular.The tensile strength,yield strength and elongation of the alloy under-60?reach260MPa,188MPa and 13.50%respectively.Compared with the tensile strength at 20°C,the tensile strength and yield strength are increased by 7.44%and 8.05%respectively,and the elongation is slightly decreased.After Al-10Si-3Cu-0.3Mg-0.2Er alloy is treated with T6,the tensile properties of the alloy at low temperature(-60°C)are significantly improved compared to the as-cast state,and the tensile strength,yield strength and elongation rate reach 368MPa,317MPa and 6.97%,an increase of 24.75%,20.08%and 75.13%respectively.At the same time,when the heat treatment conditions are the same,the tensile strength and yield strength are increased by 12.54%and 6.38%respectively,compared with room temperature(20°C)tensile,while the elongation has decreased,which has decreased by 12.33%.