Microstructural and mechanical behavior of multi-walled carbon nanotubes reinforced Al–Mg–Si alloy composites in aging treatment

Microstructural and mechanical behavior of heat treatable Al–Mg–Si (6XXX series) alloy composites reinforced with multi-wall carbon nanotubes (MWCNTs) fabricated by powder metallurgy process were investigated by SEM-EDS, XRD, tensile test and Vicker’s hardness test. As-extruded P/M 6063 alloy composites with CNT reinforcements indicated a small increment of mechanical strength compared to the monolithic 6063 alloy with no CNT before T6 heat treatment. When T6 heat treatment was applied to the specimens, the 6063 composite with CNTs showed a noticeable decrease of yield stress (YS) improvement, compared to the monolithic Al alloy. It means that Mg2Si precipitates hardening effect by the artificial aging treatment was insufficient for the composite containing CNTs. This was mainly because Mg alloying elements were diffused around CNTs and consumed to form Al2MgC2 compounds, and resulted in the incomplete matrix strengthening behavior by Mg2Si precipitation after the aging treatment.