Improved creep-aging behavior and mechanical properties of AA7150 alloy by enhancing quenching rate

This study examines the creep aging response of the AA7150 alloy subjected to various quenching rates (i.e. water quenching (WQ), oil cooling (OC), and liquid nitrogen quenching (LNQ)), elucidating their microstructural changes before and after the creep aging process through comprehensive microstructure analyses. The findings indicate that increasing the quenching rate enhances the creep strain of the alloy by elevating the vacancy concentration. Under a creep stress of 150 MPa, the LNQ sample exhibits creep strains 1.51 and 1.18 times greater than those of the OC and WQ samples, respectively. The accelerated quenching rate suppresses the agglomeration of dissolved solute atoms and elevates the vacancy density in the quenched Al alloys, thereby facilitating the formation of fine n ' precipitates while mitigating the formation of coarse n precipitates. Moreover, increasing the quenching rate reduces the width of the precipitate-free zone (PFZ). Consequently, specimens subjected to higher cooling rates contain greater quantities of fine n ' precipitates and narrower PFZs, resulting in higher strength after creep aging. Particularly, the LNQ sample exhibited outstanding mechanical properties under a creep stress of 150 MPa, with a tensile strength of 611.4 MPa, yield strength of 592.4 MPa, and fracture elongation of 14.8 %. The findings elucidate the influence of quenching rate on the creep aging behavior of the AA7150 alloy, offering a novel approach to enhance both the creep strain and strength characteristics of quenched Al alloys.