M. Ghalambaz, M. Shamanian, A. M. Eslami, M. Abdollahi, E. Abdoulvand,
Volume 41, Issue 1 (8-2022)
Abstract
This research investigated the bonding properties of AISI 321 austenitic stainless steel from microstructural, mechanical, and corrosion points of view. To obtain the optimal parameters of pulsed current gas tungsten arc welding (PCGTAW), the Taguchi method was used. A cyclic potentiodynamic polarization test evaluated the corrosion resistance of the welded samples. The optimal conditions were achieved when the background current, the pulse current, the frequency, and the percentage of the pulse on time were 50 amps, 140 amps, 5 Hz, and 50, respectively. On the other hand, the analysis of variance showed that the percentage of pulse on time equal to 36 and the background current equal to 46 amperes were the most influential factors on the surface current density of the austenitic stainless steel 321 connection using the PCGTAW process. The mechanical properties were assessed using punch shear testing. In the optimal condition, the maximum shear force and strength were 3200 N and 612 MPa, respectively. The results showed that the most critical factor affecting the bonding properties of 321 steel was the heat input.
F. Harati, S. M. Mousavizadeh, M. A. Jabbareh,
Volume 41, Issue 1 (8-2022)
Abstract
Cast AZ91 alloy is one of the most used magnesium alloys, which is sensitive to liquation in the fusion weld method,s and friction stir spot welding due to low eutectic temperature and the presence of the intermetallic compound in eutectic temperature. In this research, the liquation behavior of AZ91 alloy during friction stir spot welding was investigated. The process was carried out at two rotation speeds of 1000 and 2500 rpm and a dwell time of 1 second on the plate of AZ91 with a 10 mm thickness. Microstructural characterization was carried out using optical and scanning electron microscopes. The results showed that at low rotation speed (1000 rpm), mechanical grinding redistribution and dissolution of 𝛾-Mg17Al12 precipitates occurred. While at high rotation speed (2500 rpm), the predominant phenomenon was liquation. In this condition, the liquation initiated around the 𝛾 phase, and then the liquid re-solidified, leading to the typical eutectic structure instead of initial 𝛾 precipitates. Moreover, the liquation intensified by approaching the stirred zone. Also, the presence of liquid film along grain boundaries resulted in decreased grain boundary strength and liquation cracking.
