Second Phase Dissolution Evolution of an As-Cast Al-4.0Cu-1.0Li-0.4Mg-0.3Ag-0.1Zr Alloy during Multiple Homogenization Processes

Abstract

Homogenization treatment is vital for eliminating eutectic structure and ensuring a preferable microstructure foundation for Aluminum Lithium (Al-Li) alloys. In this paper, solidification phases in an as-cast Al-Li alloy were revealed and their evolutions during multiple homogenization processes were analyzed by means of scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and differential scanning calorimetry (DSC) analysis. The results showed that the as-cast microstructure mainly contained needlelike Al2CuLi and Al2Cu phase, large size Cu-rich phases and netlike Ag-containing phases attached to them. As the alloy homogenized by 455°C/16h, except for needle-like phases inside grains, part of phases on grain boundaries had dissolved into the matrix and exhibited rounded shapes. As homogenized by 455°C/16h+495°C/16h, Ag-containing phase had completely dissolved into the matrix while the Cu-rich phases remained and showed two different morphologies depending on whether Mg element was contained. Prolonging the second homogenization time to 28h, no obvious change occurred for the Cu-rich phase. As homogenized by 455°C/16h+495°C/20h+512°C/20h, most Cu-rich phase had dissolved into the matrix while residual phase was mainly Fe-containing phase. This proposes an effective way to eliminate various solidification phases in Al-Li alloys and identify their contents.