Microstructural development and mechanical properties of interrupted aged Al-Mg-Si-Cu alloy

Abstract

The effects of a recently developed interrupted aging procedure on the microstructural development and mechanical properties of the commercial Al-Mg-Si-Cu alloy 6061 have been studied using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and mechanical testing. This so-called T6I6 temper involves partially aging the alloy at a typical T6 temperature (the underaging stage), quenching, then holding at a reduced temperature (in this case 65°C) to facilitate further hardening (the secondary aging stage), prior to final aging to peak properties at, or close to, the initial aging (T6) temperature (the reaging stage). The T6I6 aging treatment produces simultaneous increases in tensile properties, hardness, and toughness, as compared with conventional T6. The overall improvement in the mechanical properties of 6061 T6I6 is associated with the formation of a greater number of finer, and more densely dispersed, b0 precipitates in the final microstructure. Secondary precipitation took place during the interrupted aging stage of the T6I6 temper, resulting in the formation of a large number of Guinier-Preston (GP) zones that served as precursors to the needlelike b0 precipitates when elevated temperature aging was resumed.

Effects of the artificial-aging temperature and time on the mechanical properties and springback behavior of AA6061

“…The AA6061 alloy is one of the most widely used aluminum alloys from the 6xxx series. 3 It is an age-hardenable alloy, whose mechanical properties are mainly controlled with the hardening precipitates contained in the material.…”

Effect of electropulse on solid solution treatment of 6061 aluminum alloy

“…Since the peak-aging treatment of 6061 alloy is mature, new heat treatments developed to improve the strength are seldom reported except for the T6I6 temper developed by Buha et al [7], which increased the peak hardness by 9%. In an attempt to improve the mechanical properties of the alloy, most of the studies paid attention to the modification of aging process.…”

Influence of starting temperature on differential scanning calorimetry measurements of an Al–Mg–Si alloy

“…Most of these experiments involve linear heating and are started below or around room temperature (RT). In general there are two basic types of experiment: (i) those starting directly after quenching [2][3][4]; or (ii) those starting after some pre-aging treatment and thus taking into account the influence of RT storage on precipitation kinetics [5,7,9]. For most rich Al-Mg-Si alloys a storage period longer than a few minutes after quenching has been shown to strongly retard the precipitation kinetics of the major strengthening phase β″ formed during artificial aging [10,11].…”