Influence Of Two-stage And Cu Addition On Properties Of Al-Mg-Si Conductor Rail

Al-Mg-Si(Cu)alloy is widely used in power supply system of urban rail,due to their favorable mechanical properties for its lower density,overall performance and electrical conduction.Al-Mg-Si(Cu)alloys belong to heat-treatable strengthened alloys,and their properties are strongly depended on the precipitation of coherent or semi-coherent nano-particles from the supersaturated solid solution Al matrix,while the conductivity of the alloy is determined by the content of the solution elements.During the ageing process of typical 6XXX alloys,the strength of the alloy first rise then descend with the increasing of aging time,however the conductivity shows a continuous increase.So this causes a contradiction between strength and electrical conductivity.The present supply rail must to meet the requirements of conductivity at over ageing state.The composition and aging process of alloys determine the type and amount of precipitates in Al-Mg-Si(Cu)alloy,which not only affect the strength,but also affect the conductivity.In order to understand influence of the compositions and the aging procedures on the properties of the alloy,this work was divided into two major parts:The first part was focused on two-stage ageing,and the second part was emphasized on the influence of the different Cu content on the precipitation of the Al-Mg-Si(Cu)alloy.The results show that two-stage aging can increase the peak hardness of the 6063 alloy compared with one step aging,and high hardness range of the alloy is prolonged,which is beneficial to electric conductivity to be up to standard.When two-stage ageing was employed,which was the first step aging temperature 90℃+ the second step temperature 180℃,the tensile strength,elongation and conductivity the 6063 alloy can up to 225MPa,12%and 56.83%IACS respectively,which can meet service requirements.The first stage aging temperature mainly affects the precipitation process at the initial stage of aging,which can promote the formation of GP zone and influence the number and distribution of GP zone..The two stage aging temperature controls the subsequent precipitation process,which can decides the type of the precipitates,such as needle-like P" phase and rod-like β’ phase.These precipitates determine the comprehensive properties of the alloy.The results about Cu addition indicated that the additions of Cu element can improve the peak hardness of the alloy significantly,but the conductivity of the alloy decreases with the increasing of Cu element.Al-0.8Mg-0.58Si-0.6Cu(wt.%)alloy has better comprehensive performance,which not only meets the services requirements,but also further widen the process window.Its tensile strength,elongation and conductivity can up to 225MPa,11.5%and 56.90%IACS respectively.The addition of Cu element can promote the precipitation of needle-like β" phase,and affects he ratio of different precipitates in the over aging stage.The reason of keeping the high strength of the Al-Mg-Si(Cu)alloy at the over-aging stage can attribute to the lath-like Q’ phase and retained needle-like β" phase.