Natural aging behavior of AA7050 Al alloy after cryogenic rolling

The effect of cryogenic rolling on the natural aging behavior of a commercial AA7050 aluminum alloy was investigated. Solutionized 10 mm-thick sheets were cryo-rolled to true strains of 0.5, 0.9, 1.1 and 1.4 followed by natural aging (T4 temper) at times ranging from 10 to 1000 h. Light optical microscopy (LOM), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to follow the microstructural changes upon processing. Mechanical properties were assessed by Vickers hardness measurements and tensile tests. During natural aging the hardness values increased from 100 HV to approximately 145 HV after 100 h. The strength of the undeformed specimen, naturally aged for 100 h, was much higher than that in the as-quenched state. The yield strength (YS) increased from 130 to 375 MPa (188% increase) and the increment of ultimate tensile strength (UTS) was almost 47% (321–470 MPa). A superior combination of mechanical properties was achieved for the specimen cryo-rolled to a true strain of 0.5 followed by natural aging for 1000 h (YS=611 MPa and 15% total elongation). These results suggest that a combination of cryogenic rolling with natural aging is a useful method for achieving optimized mechanical properties for the AA7050 alloy.