Post-fire material behaviour, residual properties and predictive models of recycled 6061-T6 aluminium alloys

Abstract

Aluminium alloys have been used in the past decades for a wide range of construction applications, owing to their desirable mechanical properties and recyclable nature. As many aluminium alloy structures are now approaching the end of their service life, one effective way to achieve construction sustainability is to recycle and reuse them. This paper presents an experimental investigation into the material behaviour and residual properties of recycled 6061-T6 aluminium alloys after exposure to elevated temperatures. A total of 51 coupon specimens, extracted from recycled 6061-T6 aluminium alloy square hollow sections with three recycled content ratios (30 %, 50 % and 80 %), were tested after exposure to elevated temperatures ranging from 30 ℃ (i.e. ambient temperature) to 550 ℃, with two cooling methods (natural cooling and water cooling) adopted. The experimental investigation included heating, soaking and cooling of coupon specimens as well as post-fire tensile coupon tests and fractographic analyses. The test setups, procedures and results were fully reported and the ductility, retention factors and fracture morphologies were discussed and analysed. It was found that the post-fire material properties and stress–strain curves of recycled 6061-T6 aluminium alloys exhibited obvious differences for the elevated temperatures from 300 ℃ to 550 ℃ and the influences of cooling methods were significant for the elevated temperatures beyond 400 ℃. On the basis of test data, the existing residual material property predictive models for primary 6061-T6 and 6082-T6 aluminium alloys after exposure to elevated temperatures were evaluated for the applicability to their recycled counterparts, revealing high levels of dispersion in predicting the post-fire 0.2 % proof stresses and ultimate stresses. Then, a series of new predictive models for recycled 6061-T6 aluminium alloys after exposure to elevated temperatures were proposed and shown to lead to accurate and consistent residual material property predictions. Modified Ramberg–Osgood material models were also developed and shown to well represent the measured stress–strain curves of recycled 6061-T6 aluminium alloys after exposure to elevated temperatures.

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