The impact of L12 dispersoids and strain rate on the Portevin-Le-Chatelier effect and mechanical properties of Al–Mg alloys

Abstract The 5xxx-series Al–Mg alloys are susceptible to the Portevin Le Chatelier (PLC) effect which manifests itself as stress serrations and is visible as stretcher strain markings on the surface of deformed sheets during uniaxial testing. This limits the application of 5xxx-series Al–Mg alloys in the automotive industry. Here we show that trace additions of Sc and Zr can reduce the intensity of such instabilities in Al–Mg alloys with varying Mg levels. The PLC behaviour is quantitatively examined in tensile tests for three different strain rates. It is shown that the PLC effect intensified and evolved from continuous type A to random type C bands with increasing Mg content. The addition of Sc and Zr reduced the intensity of the PLC bands and led to the occurrence of mostly continuous type A bands and a decreased intensity of stress drops at all strain rates. For all test conditions, the severity of PLC instabilities decreased with increasing strain rate. The reduction of the PLC effect with Sc and Zr addition is related to the presence of fine L12 dispersoids which trap vacancies and reduce the mobility of the Mg atoms.