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Showing 2 results for Liquation
Liquation and re-solidification in thermo-mechanically affected zone during friction stir spot welding of AZ91 alloy substrate
F. Harati, M.a. Jabbareh, S.m. Mousavizadeh,
Volume 8, Issue 2 (1-2023)
Abstract
The present research aims to study the liquation and re-solidification of liquid during friction stir spot welding of AZ91 alloy. Although friction stir spot welding is a solid-state process, the presence of Mg17Al12 intermetallic compounds results in liquation during the welding process. In this study, friction stir spot welding was performed with a tool rotational speed of 2500 rev/min and a tool dwell time of 5 seconds. The microstructural assessment was carried out by optical and scanning electron microscopes. The results showed that initiation of liquation from the inner and outer edge of the eutectic precipitates occurred based on the melting of residual eutectic. Moving toward stirred zone, a liquid film formed along the grain boundaries. The liquid re-solidified as a composite structure of α-Mg/, which α-Mg phase dispersed in γ-Mg17Al12 matrix. Also, the results showed that eutectic morphology resulting from re-solidification is related to the cooling rate. Eutectic morphology changed from granular to fibrous by increasing the cooling rate. Also, the liquid film along the grain boundaries re-solidified as a divorced eutectic.

Investigation of the effect of pulse frequency in gas tungsten arc welding (GTAW) of IN738LC nickel-based superalloy
R. Sahihi, S. M. A. Boutorabi, R. Ashiri,
Volume 11, Issue 2 (12-2025)
Abstract
The weldability of the superalloy Inconel 738LC is compromised by its susceptibility to heat-affected zone (HAZ) liquation cracking, a consequence of its high gamma-prime (γ') precipitate strength and the formation of low-melting-point eutectic phases. This study investigates the impact of Gas Tungsten Arc Welding (GTAW) current mode—comparing continuous current with pulsed current—on the microstructure, mechanical properties, and overall weldability of IN738LC. Through room-temperature tensile testing, Vickers hardness measurements, and microstructural analysis via optical and electron microscopy, it was demonstrated that pulsed current, particularly at higher frequencies, substantially mitigates liquation cracking and improves joint integrity. The pulsed technique introduces controlled thermal fluctuations that reduce the effective heat input, promoting a transition from columnar to equiaxed dendritic solidification, minimizing interdendritic segregation, and refining the distribution of MC carbides. Consequently, the weld metal exhibits enhanced tensile strength, ductility, and hardness. These findings establish pulsed GTAW as an effective strategy for suppressing cracking and improving the performance of IN738LC welded joints.

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