| Aluminum alloys are the most widely used non-ferrous metal structural materials in industry. Due to the advantages of high specific strength, excellent formability, good corrosion resistance and so on, it has been widely applied in many fields such as automotive, aerospace and high speed train. As is well known, aluminum is an excellent light-weight conductor whose conductivity ranks fourth in the common metal materials. However, its wide application in power engineering is restricted due to its low strength. Although aluminium alloys have already been applied as conductive materials, it has always been a primary concern from both industry and academia that producing Al alloys with high strength and high electrical conductivity in order to realize their wider applications as conductive materials or thermal conductive materials. Adding a small amount of Mg, Si and Cu in pure aluminium forms 6xxx series Al alloys(Al-Mg-Si-Cu) that are the most widely used Al alloys in modern industry. The electrical conductivity of Al is only slightly sensitive to elements like Mg, Si and Cu, and 6xxx series Al alloys have a low content of alloying elements, therefore Al-Mg-Si-Cu alloys become suitable to be conductive materials, especially for the applications with higher requirement on strength and electric conductivity.Adopting combined deformation and aging process, the objective of present work is to achieve Al-Mg-Si-Cu alloys with high strength and high electrical conductivity by tunning the aggregation of alloying elements before deformation and post-aging temper. Two kinds of Al-Mg-Si-Cu alloys(Mg/Si=1 and 2, but with similar total contents of alloying elements) were chosen for this study. They are respectively subjected to T6 treatment and deformation-ageing treatment, then post-ageing at different temperatures(150oC, 180 oC, 210 oC and 240oC) was conducted. The property and microstructure were investigated by hardness test, electrical conductivity test, tensile test and transmission electron microscopy(TEM). Our findings are useful in revealing the mechanism of property enhancement of Al-Mg-Si-Cu alloys processed by deformation and aging as well as the effect of pre-treatment and deformation ratios on the comprehensive property(the combination of strength and electrical conductivity) of Al-Mg-Si-Cu alloys to establish the relationship between macro-properties and microstructure evolution. The conclusions are summarized as follows:(1) The comprehensive properties of Al-Mg-Si-Cu alloys are significantly improved by combined deformation and aging process through changing the sequence of traditional T6 temper. The deformation before subsequent aging can introduce a large number of dislocations which could compensate the strength loss resulted by precipitation coarsening during subsequent aging. The dislocations have little effect on electrical conductivity while could promote the precipitation coarsening leading to an obvious increase in electrical conductivity.(2) During subsequent aging, aging temperature can affect the rate of precipitate growth and dislocation annihilation, proper tuning of which is essential in obtaining excellent comprehensive property.(3) The pre-formed solutes aggregates differ in the alloys pre-treated by natural aging and artificial ageing, resulting in the variation in density and arrangement of dislocations introduced by deformation. During subsequent ageing, the pre-existed dislocations have a marked influence on the microstructure evolution and the comprehensive property.(4) The comprehensive property enhances with increasing deformation ratio. The increase in density of dislocations and modifications of dislocation arrangements due to the increase of deformation ratio are responsible for this phenomenon. The dislocation can not only strengthen the material, but also act as fast atomic diffusion channels in subsequent aging, leading to the change of precipitation behaviors. |
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