Effect of Quenching Method on Microstructure and Properties of 7050 Aluminium Alloy Extruded Bar
Taking φ75 mm 7050 aluminium alloy bar as the research object,the samples were quenched offline and online respective-ly,and then aged.The microstructure and tensile properties of the offline and online quenched samples were analyzed and tested by OM,SEM,EDS,TEM and electronic tensile testing machine,and the results were compared.Stress corrosion test and exfoliation cor-rosion test were carried out on the two samples,and the corrosion resistance of the samples under the offline and online quenched quenching methods was compared.The results show that the amount of the second phase in the matrix of the online quenched sample is much more than that of the offline quenched sample.The precipitated phase in the offline quenched sample of 7050 aluminium al-loy bar after ageing is mainly rod-like η'phase,and there are some ηphases.A large number of entangled GP regions can be seen in the grains of online quenched samples,with some η'phase and a small amount of ηphase.Due to the low solution temperature and insufficient quenching cooling rate,the solute concentration of susaturated solid solution is reduced,and the amount of ageing precipi-tation strengthening phase is reduced,resulting that the strength of online quenched sample is reduced.The electrical conductivity,stress corrosion properties and exfoliation corrosion properties of the online and offline quenched samples meet the requirements of rel-evant standards.The two step stage ageing can effectively improve the stress corrosion resistance and exfoliation corrosion resistance of aluminium alloy,and the corrosion resistance has certain advantages over the peak ageing.
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