Mechanical and tribological behavior of severely plastic deformed Al6061 at cryogenic temperatures

In this research, Al6061 alloy was severely cryorolled up to 85% thickness reduction to study the effect of the cryorolling process on its microstructural, mechanical and tribological properties. The cryorolled Al6061 alloy was characterized by using scanning and transmission electron microscopies (SEM, TEM), X-ray diffraction (XRD) analysis, and microhardness, tensile, nano-indentation, and sliding wear tests. An improved tensile strength of the cryorolled Al6061 alloy after aging heat treatment (the CR+PA sample, 357 MPa) was observed as compared to the cryorolled sample (the CR sample, 292 MPa) and the solution treated sample (the ST sample, 150 MPa). The improved strength of the cryorolled alloy is due to the accumulation of dislocation density as a result of deformation at cryogenic temperatures and ultrafine-grained microstructure after aging heat treatment. Furthermore, in the CR sample, due to the high dislocation density and rapid atomic diffusion along dislocations, nano-sized β′ and β″ precipitates were formed. Also, the mentioned microstructural features resulted in an increase in the hardness of the CR+PA sample as shown by microhardness and nano-indentation tests. An increase in the wear resistance of Al6061 alloy as a result of cryorolling and aging was also observed. The wear mass loss for the Al6061-T6, CR, and CR+PA samples in 500 m were 63.6, 66.2 and 39.5 mgr, respectively. According to the evaluation of wear tracks and debris, for all samples, the adhesive and abrasive mechanisms were the dominant wear mechanisms.