INFLUENCE OF T6I6 TEMPER ON TENSILE AND INTERGRANULAR CORROSION PROPERTIES OF 6061 ALUMINUM ALLOY

Abstract

It is important to achieve a good combinization of high tensile properties and high intergranular corrosion resistance for 6000 series alloys in wider applications.In this paper,the effect of T6I6 temper on tensile and intergranular corrosion properties of 6061 aluminum alloy was investigated by tensile test,intergranular corrosion test,OM and TEM.The experimental results show that after T6 temper the ultimate strength and yield strength of 6061 alloy are 356.0 and 331.6 MPa respectively, but it has a serious tendency to intergranular corrosion sensitivity.It is found that pre-ageing time of T6I6 temper has no remarked effect on tensile properties of the alloy,but interrupted temperature and interrupted time have obvious effects on its tensile and intergranular corrosion properties.After T6I6 treatment,the tensile strength of 6061 aluminium alloy reaches its peak strength firstly and then decreases to a small value with the increase of interrupted time after pre-ageing at interrupted temperature of 150℃,and the corrosion mode also changes from intergranular to uniform corrosion.Higher interrupted temperature and longer interrupted time are beneficial to achieve a good combinization of tensile properties and intergranular corrosion resistance,which results from the high density of precipitates inside grains and discontinuously distributed precipitates on grain boundaries.After an optimum T6I6 treatment of 180℃×2 h+150℃×2160 h+180℃×8 h,the ultimate strength and yield strength are 348.5 and 326.9 MPa respectively,close to those after T6 temper.The corrosion mode is changed from the intergranular corrosion of 6061 Al alloy after T6 temper to a uniform etching with the etching depth about 30μm.