Effects of heat treatment and zirconium addition on grain boundary fracture of Al-5%Mg alloys with sodium

Effects of heat treatment and additional zirconium on grain boundary (GB) fracture of Al-5%Mg alloys containing sodium were investigated. As a result of the tensile test, room temperature ductility decreased as the amount of Na increased from 4 ppm to 200 ppm in the homogenized specimen. GB fracture was observed at room temperature when the alloy contained 200 ppm of sodium. On the other hand, the homogenized specimen containing 200 ppm of sodium did not show GB fracture even at 300 °C. High temperature embrittlement (HTE) was observed in the Al-Mg-4 ppm Na alloy with cold-swaging plus recrystallization heat treatment after the homogenization. HTE was partially suppressed by the addition of 0.2%Zr in an Al-Mg alloy with 3 ppm of Na, while not fully be suppressed by the addition of 0.1% Zr in an Al-Mg alloy with 2 ppm of Na. Furthermore, it was revealed that the HTE of the Al-Mg-0.1%Zr alloy with 2 ppm of Na was fully suppressed by the additional annealing at 450 °C for 5 h. It was presumed that Al3Zr precipitates is effective for the suppression of the HTE of Al-Mg alloys caused by sodium. © 2020 The Japan Institute of Light Metals