Study Of Cryogenic Thermo-mechanical Treatment Behavior Of 6016 Aluminium Alloy

Aluminium alloys are given preference to lightweight materials. Producing Al alloys with high strength and toughness is the key to enlarge its structural applications. It is said that the thermo-mechanical treatment has a great influence on mechanical properties of Al alloys. The present work was undertaken to deeply investigate the cryogenic thermo-mechanical treatment behavior of the 6016 aluminium alloy subjected to solid solution, pre-aged and T6 treatments. After cryo-rolling and subsequently low temperature aging, the mechanical properties and microstructural evolution of the three states of alloys vary from each other.The yield strength(YS) of the solution treated Al alloy subjected to cryo-rolled was improved to 6.5 times higher, but the elongation decreased severely. The later was improved after low temperature aging. It was observed from the microstructural characterizations that the dynamic recovery was suppressed during cryo-rolling. The improved strength are due to the refined microstructure with high density dislocations and substructures. Precipitate, recovery and partial recrystallization occur during aging, which is essential for good elongation.The YS of the pre-aged Al alloy subjected to cryo-rolled was even higher with lower elongation. But its strength and elongation were improved simultaneously after low temperature aging. It was thought that the combined effect of age-hardening, dislocation and grain boundary strengthening contributed to the enhanced strengthen. The cryo-rolled Al alloy of pre-aged accelerated the precipitates of strengthening phases during aging, which further improved the mechanical properties.The cryo-rolled Al alloy of T6 treatment achieved the highest YS, but with the lowest elongation. The age-hardening made a major contribution to the strength. The low temperature aging didn’t improve the mechanical properties of the cryo-rolled alloy further, which was due to the precipitates with weaker strengthening effect formed during aging.Contributions to the strength of the 6016 Al alloy from various strengthening mechanisms were discussed. It was found that during cryogenic thermo-mechanical treatment, the contribution of age-hardening to the strength increased with improving extent of aging before cryo-rolling, whereas, the contribution of dislocation and grain boundary strengthening decreased.