ABSTRACT
Molecular dynamics was applied to simulate ECAP of single-crystal magnesium at room temperature. Four samples with different orientations were processed, and the grain structure, grain fragmentation, slip systems, strain, and twin formation were analyzed. The initial orientation played a substantial role in the strain and deformation experienced by the samples during both stages of deformation. Compressions initially occurred before extrusion, and simple shear occurred in the deformation zone during extrusion. The samples nucleated a { 10 1 ¯ 2 } tension twin during compression, and the tension twin grew to immediately cover the entire sample, effectively changing the orientation of the sample. Additionally, stacking faults acted as a precursor for the { 10 1 ¯ 2 } tension twin. The strain was strongly correlated with the shear factor, that is, a high shear factor resulted in low strain. Moreover, discrepancy occurred between theoretical and actual shear strain due to two factors. First, theoretical shear is considered to be simple shear occurring entirely in the deformation zone; it does not consider the shear strain due to the normal stress in the compression phase. Second, deformation is considered to be homogenous and isotropic, and it does not take into account the initial grain orientation and the anisotropic nature of magnesium.
ABSTRACT
Laser metal deposition (LMD) is one of the manufacturing processes in the industries, which is used to enhance the properties of components besides producing and repairing important engineering components. In this study, Stellite 6 was deposited on precipitation-hardened martensitic stainless steel (17-4 PH) by using the LMD process, which employed a pulsed Nd:YAG laser. To realize a favor deposited sample, the effects of three LMD parameters (focal length, scanning speed, and frequency) were investigated, as well as microstructure studies and the results of a microhardness test. Some cracks were observed in the deposited layers with a low scanning speed, which were eliminated by an augment of the scanning speed. Furthermore, some defects were found in the deposited layers with a high scanning speed and a low frequency, which can be related to the insufficient laser energy density and a low overlapping factor. Moreover, various morphologies were observed within the microstructure of the samples, which can be attributed to the differences in the stability criterion and cooling rate across the layer. In the long run, a defect-free sample (S-120-5.5-25) possessing suitable geometrical attributes (wetting angle of 57° and dilution of 25.1%) and a better microhardness property at the surface (≈335 Hv) has been introduced as a desirable LMDed sample.
ABSTRACT
The 5083 and 6061(T6) aluminum (Al) alloys are widely used in transportation industries and the development of structural designs because of their high toughness and high corrosion resistance. Friction stir welding (FSW) was performed to produce the dissimilar welded joint of Al5083-Al 6061(T6) under different welding parameters. However, softening behavior occurred in the friction stir welded (FSWed) samples because of grain coarsening or the dissolution of precipitation-hardening phases in the welding zone. Consequently, this research intended to investigate the effect of the post-weld heat treatment (PWHT) method on the mechanical property improvement of the dissimilar FSWed Al5083-Al6061(T6) and governing abnormal grain growth (AGG) through different welding parameters. The results showed PWHT enhanced the mechanical properties of dissimilar joints of Al5083-Al6061(T6). AGG was obtained in the microstructure of PWHTed joints, but appropriate PWHT could recover the dissolved precipitation-hardening particle in the heat-affected zone of the as-welded joint. Further, the tensile strength of the dissimilar joint increased from 181 MPa in the as-welded joint to 270 MPa in the PWHTed joint, showing 93% welding efficacy.
