Phase Transformation Behavior of Ultrasonic-treated 7085 Aluminum Alloy During Heat Treatment

Abstract

The transformation behavior of secondary phases in conventional ingot and ultrasonic ingot during heat-treatment process were investigated by OM, SEM, EDS and DSC. Crystalline phase transition was observed by SEM with in situ heating station. The experiment results indicate that the ultrasonic melt treatment transforms from columnar crystals to equiaxed crystals, and obtains fine and uniform grains. The melting enthalpy of ultrasonic ingot is 4.60J/g, while the melting enthalpy of conventional ingot is 6.52J/g, combined with EDS analysis results, θ phase and T phase are found to be reduced by 29% after ultrasonic melt treatment. The secondary phases in the ingots include θ phase, T phase, Al3Fe phase and Mg2Si phase. θ phase is dissolved into matrix gradually, T phase transforms to S phase and is dissolved into matrix at high peak temperature, Al3Fe phase transforms to Al7Cu2Fe phase at low peak temperature and remains in the ingots, Mg2Si phase changes nothing during DSC analysis process.

Keywords

• ultrasonic casting
• crystalline phase
• DSC analysis
• heat treatment