Formation mechanism of the quasicrystal in Al-Cu-Mg-Zn aluminum alloy resistance spot weld

Abstract

In this study, the formation mechanism of the quaternary quasicrystal phase (59.59Al-8.85Cu-16.85Mg-14.71Zn, at. %) in the Al-Cu-Mg-Zn alloy resistance spot welding nugget was revealed. Transmission electron microscopy shows the quasicrystal phase was located at the inner-dendrite zone of which selected area electron diffraction spot exhibits a typical pattern of an icosahedral quasicrystal (fivefold axes). During the cooling process, Cu-Mg-Zn solute enriched within the remnant liquid at the inter-dendrite zone with short-range-ordered clusters structure. Instead transforming to typical crystalline phases, this undercooled remnant liquid forms the icosahedral quasicrystal phase due to the rapid cooling rate of resistance spot welding. This study shows the feasibility of acquiring massive quasicrystal phase in commercially-used aluminum alloy under common processing condition.