Microstructural evolution of new type Al-Zn-Mg-Cu alloy with Er and Zr additions during homogenization

A comprehensive study on the microstructural evolution of a new type Al-Zn-Mg-Cu-Er-Zr alloy duringhomogenization was conducted by optical microscope,scanning electron microscope,transmission electron microscopy and X-raydiffraction analysis.The results show that serious segregation exists in as-cast alloy,and the primary phases are T(AlZnMgCu),S(Al2CuMg)and Al8Cu4Er,which preferentially locate in the grain boundary regions.The soluble T(AlZnMgCu)and S(Al2CuMg)phases dissolve into the matrix gradually during single-stage homogenized at465°C with prolonging holding time,but the residualAl8Cu4Er phase cannot dissolve completely.Compared with the single-stage homogenization,both a finer particle size and a highervolume fraction of L12-structured Al3(Er,Zr)dispersoids can be obtained in the two-stage homogenization process.A suitablehomogenization scheme for the present alloy is(400°C,10h)+(465°C,24h),which is consistent with the results of homogenizationkinetic analysis.

Microstructure, mechanical properties and corrosion behavior of commercial 7N01 alloys

The effect of grain morphology and precipitates on mechanical properties and corrosion behavior of two commercial 7 N01 alloys was studied using transmission electron microscopy(TEM) and scanning electron microscopy(SEM) equipped with electron backscatter diffraction(EBSD). Results showed that the recrystallization degree of the outer surface of 7 N01-I alloy was lower than that of 7 N01-II alloy. The main strengthening precipitates of two alloys were mainly η’ phases. The grain boundary precipitates(GBPs) of 7 N01-I alloy distributed discontinuously, while those of 7 N01-II alloy distributed continuously. The strength of two 7 N01 alloys was similar, but the maximum corrosion depth of 7 N01-I alloy was less than that of 7 N01-II alloy, because the discontinuous GBPs and the lower recrystallization degree of outer surface of 7 N01-I alloy were favorable for improving corrosion behavior. Different models of strengthening mechanism were discussed, and the corrosion behavior was correlated with microstructure.

Dislocation evolution and induced precipitation on corrosion resistance of a novel Al-Mg-Zn-Er-Zr alloy during hot compression

Al-Mg-Zn-Er-Zr alloy was compressed in temperature range from 300 to 500℃to investigate the microstructure evolution.Molecular dynamics simulations were used to study the mechanical behavior and dislocation evolution.The results showed that mobile dislocations are widely distributed in alloys and make important contributions to coordinate compressive deformation.The sessile dislocations hinder the deformation,and the content is about 1/20 of that of mobile dislocations.Continuous dynamic recrystallization(CDRX)is considered to be the main recrystallization mechanism.The accumulation of dislocations can provide element diffusion channels and driving force forτ(Mg_(32)[Al,Zn]_(49))phase precipitation,resulting in the forced precipitation of discontinuousτphase to replace the continuousβphase(Al_(3)Mg_(2)),which reduces the corrosion potential,resulting in increased corrosion resistance.

Mechanical properties and corrosion behavior of a new RRA-treated Al-Zn-Mg-Cu-Er-Zr alloy

The effect of various retrogression and re-aging(RRA)treatments on mechanical properties and corrosion behavior of a new type Al-Zn-Mg-Cu-Er-Zr alloy was investigated by microhardness testing,tensile testing,intergranular corrosion(IGC)and exfoliation corrosion(EXCO)testing.The results show that the RRA treatment can effectively improve the IGC and EXCO resistance with less strength sacrificing because the grain interior precipitates and the grain boundary precipitates are similar to that of T6 temper and T73 temper.Meanwhile,as the microhardness of the retrogressed alloy reaches the peak value during the retrogression at 170℃,the corresponding RRA-treated alloy possesses the better strength,but the corrosion resistance is poor in comparison with that of the retrogression at 190℃.The optimal combination of strength,IGC and EXCO resistance is obtained after retrogression at 180℃for 60 min.Moreover,for different heat treatment tempers,the corresponding micros true tural evolution of the precipitates including Al_(3)(Er,Zr)particles was also discussed in detail.