Effect of Heat Treatment on Yield Point Elongation and P- L Effect in 5182 Al-Mg Alloys

摘要

Influences of the temperature of the solution treatment and cooling rates from the temperature of the solution treatment on the yield point elongation and Portevin Le Chatelier ( P-L )effect were studied in detail in commercial 5182(Al-4.4 % Mg) alloys. It was found that, if the specimens were cooled in furnace after the solution treatment at 450℃, propagation of Lueders band induced P-L effect in the region just behind the Lueders band front, because Lueders strain exceeded the critical strain, ε_c of the P-L effect in this region. For this reason, stress strain curves of such materials were severely serrated already in the flat region representing yield point elongation. During propagation of Luders band, which was thus accompanied also by the propagation of parallel bands due to P-L effect, irregularities were formed on the sides of the tensile test specimens. Since they induced local concentrations, they readily triggered P-L effect again at higher tensile strain. For this reason, in the specimen cooled in furnace, in which large yield point elongation was observed, serrated yielding started at smaller tensile strain than in the specimen quenched into water. Thus, although it is well known that yield point elongation is in itself undesirable, yield point elongation is not desirable, also because it enhances also the formation of parallel bands.