Residual-stress relaxation mechanism and model description of 5052H32 Al alloy spun ellipsoidal heads during annealing treatment

Abstract

Marginal-restraint mandrel-free spinning is an advanced technology for manufacturing ellipsoidal heads with large diameter-thickness ratios. Nevertheless, the spinning-induced residual stress, which greatly influences the in-service performance of spun heads, should be removed. In this study, the effects of annealing on the residual-stress relaxation behavior of 5052H32 aluminum alloy spun heads were investigated. It is found that the residual stress first rapidly decreases and then remains steady with the increase in annealing time at the tested annealing temperatures. The relaxation of the residual stress becomes increasingly obvious with the increase in annealing temperature. When the annealing temperature is less than 220 °C, there are no obvious changes in grain size. Moreover, the spinning-induced dislocations are consumed by the static recovery behavior, which decreases the residual stress during annealing. When the annealing temperature is approximately 300 °C, the broken grains transform into equiaxed grains. In addition, static recrystallization and recovery behaviors occur simultaneously to promote the relaxation of the residual stress. Considering the different stress relaxation mechanisms, a model based on the Zener-Wert-Avrami equation was established to predict the residual-stress relaxation behavior. Finally, the optimized annealing temperature and time were approximately 300 °C and 30 min, respectively.

Evolution of Microstructure, Mechanical Properties and Residual Stress of a Cold Rolled Invar Sheet Due to Heat Treatment

“…It can be observ tensile stress developed along the RD, while compressive stress developed along t There was no notable decrease in residual stress for the specimens annealed at 400 500 °C; this was because neither recovery nor recrystallization took place. The re process resulted in the rearrangement and annihilation of dislocations in the spe and there was a very strong correlation between dislocation density and residua [17,[20][21][22]. From [20][21][22], one can expect a rapid transformation of elastic strain, release of the residual stress, at early stages of recovery when dislocation density high.…”

“…The re process resulted in the rearrangement and annihilation of dislocations in the spe and there was a very strong correlation between dislocation density and residua [17,[20][21][22]. From [20][21][22], one can expect a rapid transformation of elastic strain, release of the residual stress, at early stages of recovery when dislocation density high. Similarly, the specimen annealed at 700 °C released 46% and 59% of the r stress formed during cold rolling along the RD and the TD, respectively, due to re Judging from the large reduction in the residual stress with recovery alone, one c cessfully control the residual stress of a cold-rolled Invar sheet with a limited reduc the strength of the sheet.…”

“…It is known that the underlying factors that contributes to changes in the mechanical properties of a material can readily affect the residual stress of the material. In particular, heat treatment based metallurgical processes such as recovery and recrystallization can not only change the mechanical properties of an alloy, but also release residual stress in the alloy [16][17][18][19][20][21][22]. However, unwary heat treatment should be avoided because these processes, which are central to the alleviation of cold rolling induced residual stress in Invar sheets, can result in undesirable changes in the microstructures and mechanical properties of the sheets.…”