Response of A356 to warm rotary forming and subsequent T6 heat treatment

TL;DR

This study investigates how rotary forming at elevated temperatures and subsequent T6 heat treatment affect the microstructure and hardness of A356 aluminum alloy, revealing stability up to 144°C and the impact of deformation on hardness.

Contribution

It provides new insights into the microstructural effects of warm rotary forming and heat treatment on A356, especially regarding hardness changes and eutectic phase behavior.

Findings

A356 is stable up to approximately 144°C.

Decreased macrohardness correlates with time at elevated temperature.

Deformation mainly affects hardness through changes in the Al-Si eutectic phase.

Abstract

The through-process microstructural effects in A356 subjected to rotary forming at elevated temperatures have been investigated. Macro and micro-hardness testing have been used extensively to track changes in the material from the as-cast state to as-formed, and T6 heat treated. Targeted thermal treatments have been used to isolate the effects of mechanical deformation through comparative measurements. These measurements include macro and micro hardness measurements, Energy-dispersive X-ray analysis and examination of eutectic-Si particle size and morphology. The results indicate that the as-cast material is stable up to approximately 144{\deg}C, with the rotary formed material exhibiting decreased macrohardness in-line with the time spent at elevated temperature. Post heat treatment, there was a significant decrease in hardness with increased levels of deformation. Results indicate that precipitation hardening is not appreciably affected by rotary forming, and the principal cause for the drop in hardness with deformation is due to the condition of Al-Si eutectic phase.