On the intermetallic constituents in the sodium-induced edge cracking of hot-rolled AA5182 aluminum alloys

Abstract

ABSTRACT The productivity and recovery of hot-rolled Al-Mg-Mn sheets often suffer from sodium-induced edge cracking. In this study, AA5182 ingots with different levels of Na were prepared by direct-chill (DC) casting, and were then subsequently subjected to homogenisation and hot-rolling processes. The edge crack occurrence during hot rolling in the pass #11 (84% reduction) and pass #18 (96% reduction) was investigated, with special attention paid to the impact of intermetallic constituents in the ingot subsurface region, where all edge cracks were initiated. Correlations between the susceptibility to edge cracking, enriched intermetallic constituents in the inverse segregation zone, Mg2Si cavitation, meniscus bands, and Na contamination were observed. The results revealed that Fe-rich intermetallic particles were not involved in crack formation, while Mg2Si particles had a strong tendency to debond from the Al matrix and form cavities at the edges of the rolled strip. The higher the Na content, the more severe the Mg2Si cavitation, and consequently, the higher the susceptibility to edge cracking. Numerous debonded Mg2Si particles contaminated with Na in the subsurface region provided favourable conditions for crack initiation and propagation. The role of the meniscus bands on the large and profound edge cracks was also elaborated.