Simultaneously Enhanced Strength and Ductility of Al–Mg–Si Alloys during Aging Process Induced by Electro-Pulsing Treatment

Most methods used for strengthening metallic materials, such as thermal-mechanical treatment, will sacrifice the ductility. A novel technology, electric pulsing treatment (EPT), is applied to break this trade-off, which produces an Al–Mg–Si alloy with superior ductility and higher strength within only 560 ms. Systematic electron microscopy characterization and finite element simulation reveal that EPT promotes the formation of clusters Mg2(Si,Cu)3 and sub-grain boundaries. The results of quantitative calculation indicate that the dislocation entanglement is delayed due to the existence of clusters and longer dislocation glide distance, so that ultimate strength is fully improved. Moreover, the superior ductility is mainly governed by sub-grains which lead to higher mobile dislocation density, appearance of new crystal orientations, and prevention of crack propagation. Thereupon, this interesting finding paves the way in developing the Al–Mg–Si alloy with higher mechanical properties efficiently.

Influence of Predeformation on Mechanical Behavior of Hastelloy C-276

The accurate prediction of springback is a subject of major concern during the sheet metal forming. In this study, the recovery behavior of Hastelloy C-276 sheet under different amounts of pre-strain has been investigated by uniaxial cyclic tensile tests. The total springback during unloading could be separated into a linear springback and a nonlinear springback. The percentage of nonlinear recovery to the total recovery increased as the pre-strain increased. Both unloading and reloading elastic moduli decreased as the pre-strain increased, which affected the springback phenomenon significantly. Nonlinear recovery could be explained by the movement of dislocations in the reverse direction. The decrease of unloading elastic modulus is mainly related with the dislocation motion and the mobile dislocation density.

Evaluation of Creep Deformation Mechanism of Heat Resistant Steel by Stress Change Test

In order to evaluate creep deformation mechanism of heat resistant steels, stress change tests were conducted during creep tests. In this study, it was confirmed that the dislocation behavior during the creep tests was in viscous manner, because no instantaneous plastic strain was observed at stress increments. Transient behavior was observed after stress changes for all kinds of steel in this work. Mobility of dislocation was evaluated by the observed backward creep behavior after stress reduction. Internal stress was evaluated by the change of creep rate in stress increment, and mobile dislocation density was evaluated with the estimated mobility of dislocation and the change of creep rate in stress increment. It was found that the variation of mobile dislocation density during creep deformation showed the same tendency as the variation of creep rate. Therefore mobile dislocation density is the dominant factor that influences the creep rate variation in creep deformation of heat resistant steels investigated in this work. The mobility of dislocation showed a good correlation with 1/T and it is related with the amount of solute Mo that is a solution strengthening element. Microstructure of crept specimens was observed by TEM to discuss the validation of these results.