The effect of Mg precipitation on the mechanical properties of 5xxx aluminum alloys

Industrially produced continuous cast (CC) aluminum alloys AA5182 and AA5052 were heat-treated at a low temperature of 182 °C for different times (30 and 100 h). Samples from the hot band (hot band in continuous cast process is produced through hot rolling of the materials at relatively high temperatures, usually from 490 to 310 °C) and the heat-treated materials were prepared for microstructure examination, chemical composition analysis, electrical resistivity testing and tensile testing. Particle structures of CC5182 alloy show precipitation along the grain boundaries after this low temperature heat-treatment. The particles were identified by SEM analysis to be Mg precipitates (Mg2Al3). Due to the Mg precipitation, electrical resistivity, elongation and ultimate tensile strength decreased. As the interaction between Mg solute atoms in solid solution and mobile dislocations decreases due to precipitation, the magnitude of the stress drop in the serrations decreases and the critical strain for the onset of serrated yielding increases in CC5182 alloy. These phenomena do not occur in CC5052 alloy since precipitation either does not occur or is much weaker in this alloy. An inverse serrated yielding behavior, which is characterized by an increase in the critical strain for the onset of serrated yielding with a decrease in strain rate, occurs in CC5182 alloy but not in CC5052 alloy. This inverse behavior is believed to be related to precipitation during tensile deformation in CC5182 alloy.