High pressure induced precipitation in Al7075 alloy

TL;DR

This study investigates how high pressures affect the microstructure and strength of Al7075 alloy, revealing pressure-induced precipitate formation and defect density increases that enhance its mechanical properties.

Contribution

It provides new insights into the microstructural evolution of Al7075 alloy under high pressure, including precipitate nucleation and defect behavior, using in situ XRD and TEM techniques.

Findings

High pressure increases defect density and precipitate formation.

Non-hydrostatic pressure causes defect nucleation and grain texturing.

Pressure cycling enhances alloy strength through microstructural changes.

Abstract

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 high strain rate impact, which involves high pressures. Here we use diamond anvil cells to study the behavior of Al-based Al7075 alloy under quasi-hydrostatic and non-hydrostatic pressure up to ~53 GPa. In situ X-ray diffraction (XRD) and pre- and post-compression transmission electron microscopy (TEM) imaging are used to analyze microstructural changes and estimate high pressure strength. We find a bulk modulus of 75.2 +- 1.9 GPa using quasi-hydrostatic pressure XRD measurements. 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 led to the nucleation and growth of many precipitates. The significant increase in defect and precipitate density leads to an increase in strength for Al7075 alloy at high pressures.