Effect Of Rare Earth Element Er And Heat Treatment Process On Microstructure And Properties Of Al-Si Conductive Aluminum Alloy

Aluminum alloy is one of the most widely used non-ferrous metal materials in the industry.It is widely used in aerospace,machinery manufacturing,shipping,power and other industries.Al-Si series alloys have good casting properties,strong welding properties,excellent electrical and thermal conductivity,and are often used as overhead power lines materials.However,this kind of material has poor conductivity and mechanical properties,and cannot meet the performance requirements of specific places.Therefore,it is very important to develop a high-strength,high-conductivity aluminum alloy material.In this paper,hypoeutectic Al-Si alloy was selected as the research object,the rare earth element Er was added to this type of alloy,and then different heat treatment processes were used to obtain an aluminum alloy conductive material with excellent comprehensive performance.In this experiment,five experimental alloys,Al-4Si,Al-4Si-0.2Er,Al-4Si-0.5Er,Al-4Si-1 Er and Al-4Si-1.5Er,were prepared in a crucible resistance furnace.Through scanning electron microscope?SEM?,X-ray diffractometer?XRD?,optical microscope?OM?and other testing methods to detect the microstructure and phase composition of the alloys.The electrical conductivity of the alloys were tested by the four-electrode method,and the mechanical properties of the alloys were tested by a universal tensile tester and a micro vickers hardness tester.First,the effects of different Er contents on the secondary phase morphology,constituents,quantity,and size of as-cast and as-extruded alloys were studied,and their electrical conductivity and mechanical properties were tested.Subsequently,the as-cast and as-extruded alloys were heat treated.The heat treatment processes were:homogenization at 500?and 540?,T6 heat treatment?Sold solution treatment at 500?for 1h,water quenching+artificial aging at 220??.The microstructure and properties of the alloys were further tested and their changes were observed,and the mechanism of action of rare earth element Er and heat treatment process on electrical and mechanical properties were studied.Finally,the Al-Si-Er alloy with the best electrical and mechanical properties was obtained by combining all factors.The experimental results showed that the phase constituents of as-cast Al-4Si alloy were:a-Al phase and eutectic silicon phase.After adding Er element in the as-cast alloys,new phases Er Si₂ and Al₃Er appeared in the alloys.The morphology of the phases were mainly semi-continuous and band-like,segregating at the grain boundaries.The conductivity of Al-4Si-0.2Er alloy was 42.4%IACS,which was slightly lower than that of Al-4Si alloy.After adding the Er element,the hardness of the as-cast alloys showed an approximately straight upward trend.The hardness of the Al-4Si-0.2Er alloy was 49.5HV,the hardness of Al-4Si-1.5Er alloy reached the highest value of 55.8HV,nearly 24%higher than that of Al-4Si alloy.The phase constituents of the as-extruded alloy were unchanged,but the morphology of the second phase had changed.The eutectic silicon phase had changed from acicular and elongated to granular,and the new phases Er Si₂and Al₃Er had changed from semi-continuous and band-like shapes to worm-like and blocky.In terms of alloy conductivity,the conductivity of Al-4Si-1 Er alloy reached the highest value,which was 53.0%IACS,and remained stable compared with the extruded Al-4Si alloy,but the mechanical properties were slightly lower.Considering the balance between electrical and mechanical properties of the alloys,the electrical conductivity of Al-4Si-0.2Er alloy was 51.6%IACS,which was slightly lower than that of Al-4Si alloy,but the mechanical properties of Al-4Si-0.2Er alloy was higher.The tensile strength was 119.2 MPa,the elongation was 38.3%,and the hardness was 43.8 HV.The rare-earth element Er could improve the mechanical properties of the alloys while maintaining the relatively stable conductivity of the as-extruded Al-Si alloys.Heat treatment could significantly improve the electrical conductivity of the alloys,especially,it was better for the alloys with Er element.When the heat treatment process was500?×1h with the furnace cooling,the mechanical properties of the alloys were improved while ensuring the electrical conductivity.The conductivity of Al-4Si-1Er alloy was 56.0%IACS,the tensile strength was 93.1MPa,the elongation was 52.8%,and the hardness was34.2HV.Compared with Al-4Si alloy,the tensile strength was increased by nearly 8%.When the heat treatment process was 540?×1h with the furnace cooling,the conductivity of Al-4Si-0.2Er alloy reached the highest value of 56.4%IACS,which exceeded that of Al-4Si alloy.The tensile strength of Al-4Si-0.2Er alloy was 87.8MPa,the elongation was 36.2%.The hardness reached the highest value of 36.0HV,which was nearly 7.8%more than that of Al-4Si alloy.The electrical conductivity and mechanical properties of the alloys were improved simultaneously.T6 heat treatment could improve the mechanical properties of the alloys to the maximum extent while ensuring the conductivity of the alloys.The conductivity of Al-4Si-1Er alloy was55.0%IACS,which was stable compared with T6 state Al-Si alloy.The finely dispersed second phase particles in the alloy structure made the mechanical properties of the alloys significantly improved,and the mechanical properties of Al-4Si-x Er alloy were higher than Al-4Si alloy.Considering the balance between electrical conductivity and mechanical properties,the overall performance of Al-4Si-1Er alloy was the best.The tensile strength of Al-4Si-1Er alloy was 103.5MPa,the elongation was 34.5%,and the hardness was 35.3 HV.Therefore,through the research in this paper,an aluminum alloy conductive material with excellent comprehensive performance was successfully prepared.The optimal addition amount of rare earth element Er was 1%.The Al-4Si-1Er alloy had excellent electrical conductivity and mechanical properties in T6 heat treatment state.