Influence of Quench Rate on Crack Sensitivity of AA6060 Two-Chamber Extrusion Profile during Axial Compression

Experiment was carried out to investigate the influence of quench rate on the axial compression property of AA6060 two-chamber extrusion profile by comparing the compressed-air quench and water quench. It reveals that the higher quench rate is required for the axial compression in contrast to the axial tension. And the crack sensitivity during the compression deformation has no single correlation to the tensile properties. The optical microscopy and transmission electron microscopy studies were conducted to correlate the microstructure and fracture characteristics. It indicates that the primary cracks are both present in the valley of tensile surface and inside the tensile area. The primary cracks on the surface are because of the strain localization, and the intermetallic particles (AlFeSi) initiated the micro-cracks inside the tensile area. Intergranular primary crack is favored when AlFeSi particles, grain boundary misorientation and intense slip band work together. The comparison of two quench conditions shows low quench rate results in high rate grain precipitates and high sensitivity to crack during the compression and bend. It attributes to cohesive bonds weakening between the grains when a large amount of precipitates occur on the grain boundary. Intergranular ductile fracture mechanism is unlikely present in water quench materials because of the low matrix strength combined with the weak population of grain boundary particles.