Effect of trace germanium on microstructure and quenching sensitivity of 7056 aluminum alloy

Abstract

The effect of trace Ge on the microstructure and quenching sensitivity of 7056 aluminum alloy was studied by mechanical tensile and end quenching experiments, combined with some analysis methods such as metallographic observation, hardness test, conductivity test, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The results show that the trace element can refine the alloy grain sizes,the grain size is reduced from 137μm to 114μm; the addition of trace Ge formes coarse Mg2Ge phase on the grain boundary and inhibits the formation of the T phase.In addition, compared with the Ge-free alloy, the width of the precipitation free zone of the Ge-bearing alloy becomes narrow, and is decreased from 190nm to 90nm, and the size of the precipitated phase at the grain boundary is reduced.The trace addition of Ge could reduce the quench sensitivity of alloy, increased the quenching depth of the alloy about 25%,which may be caused by the addition of Ge which changes the number and size of η equilibrium phase during slow cooling; the addition of Ge reduces the free vacancy concentration in the alloy, non-uniform nucleation and growth of the η equilibrium phase at the defect are suppressed, which increases the number of strengthening η' precipitates after aging.Thus the drop in the strength is decreased during slow quenching,which increases the hardenability of the alloy.

Keywords

• 7056 aluminum alloy
• Ge
• quenching sensitivity
• vacancy concentration