Study on hot deformation behavior and microstructure evolution of cast-extruded AZ31B magnesium alloy and nanocomposite using processing map

The hot deformation behavior and microstructural evolution of cast-extruded AZ31B magnesium alloy and nanocomposite have been studied using processing-maps. Compression tests were conducted in the temperature range of 250–400 °C and strain rate range of 0.01–1.0 s⁻¹. The three-dimensional (3D) processing maps developed in this work, describe the variations of the efficiency of power dissipation and flow instability domains in the strain rate ($\dot{\epsilon }$) and temperature (T) space. The deformation mechanisms namely dynamic recrystallization (DRX), dynamic recovery (DRY) and instability regions were identified using processing maps. The deformation mechanisms were also correlated with transmission electron microscopy (TEM) and optical microscopy (OM). The optimal region for hot working has been observed at a strain rate ($\dot{\epsilon }$) of 0.01 s⁻¹ and the temperature (T) of 400 °C for both magnesium alloy and nanocomposite. Few instability regimes have been identified in this study at higher strain rate ($\dot{\epsilon }$) and temperature (T). The stability domains have been identified in the lower strain rate regimes.     

Molecular dynamic modelling of fatigue crack growth in aluminium using LEFM boundary conditions

A molecular dynamic (MD) model of a crack in pure aluminium has been developed with isotropic Linear Elastic Fracture Mechanics (LEFMs) boundary displacements that simulates the fatigue crack growth process. The model consists of a cylindrical region filled with atoms around a crack tip and subject to boundary displacements that change due to cyclic loading. A sinusoidal load that produced a $K_{\max }=1.0\text{MPa}\sqrt{\text{m}}$ was applied to produce fatigue crack growth using three different atomic potentials for aluminium at T = 20 K, and a range of different K_min. Each run consisted of the application of fifteen or more loading cycles. In some cases, the crack tip was seen to advance in each cycle typical of fatigue, however, growth was smooth and continuous during the entire cycle with contraction occurring during the unloading phase of the cycle. The model contained 3 × 10⁶ atoms and had a diameter and width of 20 nm. This width was just large enough for fragments of sessile dislocations to form and couple with the glissile dislocations emitted from the crack tip, resulting in work hardening about the crack tip. The model was oriented for cracking on the {1 1 0} plane in the 〈1 0 0〉 direction. Crack advance was observed to be due to a combination of dislocation emission and atomic separation.