High pressure deformation induced precipitation in Al–Zn–Mg–Cu alloy (Al7075)

Precipitate-matrix interactions govern the mechanical behavior of precipitate strengthened Al-based alloys. These alloys find a wide range of applications ranging from aerospace to automobile and naval industries due to their low cost and high strength to weight ratio. Structures made from Al-based alloys undergo complex loading conditions such as impact and shock. Understanding the microstructural changes in Al-alloys under extreme conditions is challenging due to the fast time scale of the experiments. Here, we study the high-pressure behavior of Al7075 alloy separately from the high strain-rate behavior using quasi-static experiment in a diamond anvil cell. We combine in situ X-ray diffraction (XRD) and pre- and post-compression transmission electron microscopy (TEM) imaging to analyze microstructural changes and estimate high pressure strength. XRD showed that non-hydrostatic pressure leads to a significant increase in defect density and peak broadening with pressure cycling. XRD mapping under non-hydrostatic pressure revealed that the region with the highest local pressure had the greatest increase in defect nucleation, whereas the region with the largest local pressure gradient underwent texturing and had larger grains. TEM analysis showed that pressure cycling leads to the nucleation, growth and significant increase in density of precipitates. The significant increase in precipitate density was due to the destabilization of solid solution atoms under high pressure and led to an increase in strength for Al7075 alloy at high pressures.