TIG Welding Remanufacturing of ZM5 Magnesium Alloy Deposited Layers

Literature Overview

This research by Yao Jukun and colleagues from the Academy of Armored Force Engineering and Jiangsu Institute of Technology, published in China Surface Engineering (2015, Vol. 28, No. 4), explores the feasibility of using manual TIG welding as a remanufacturing technique for ZM5 (Mg-5Al) magnesium alloy components. Funded by the Equipment "Twelfth Five-Year Plan" pre-research fund and the Army Military Research "Twelfth Five-Year Plan," this work addresses a practical industrial need: the repair and functional enhancement of magnesium alloy parts through deposited overlay layers. The study examines both single-pass and multi-pass deposited layers, characterizing their microstructure, phase composition, hardness, and tribological properties.

Microstructural Characterization

The deposited layers are composed of alpha-Mg phase and beta-Mg17Al12 intermetallic phase, which is the equilibrium phase assemblage for the ZM5 alloy system. A notable finding is that the deposited layer grain size is significantly refined compared to the base metal. This grain refinement is attributed to the rapid solidification rates in the weld pool, which promote high nucleation rates and suppress grain growth. In contrast, the HAZ exhibits coarsened grains, a consequence of the thermal cycle exceeding the recrystallization temperature of the base metal without the subsequent rapid cooling that produces refinement.

The hardness results demonstrate that the single-pass deposited layer achieves hardness values exceeding 80 HV0.05, while the multi-pass layer reaches approximately 77 HV0.05. Both values are superior to the base metal, confirming the surface hardening effect of the welding process. The HAZ hardness is comparable to the base metal, indicating that the thermal cycle did not significantly alter the phase distribution in that region.

Tribological Performance

The friction and wear testing reveals an important distinction between the deposited layer and the base metal. The deposited layer exhibits predominantly abrasive wear behavior with an average friction coefficient of 0.48, while the base metal shows predominantly adhesive wear with a lower average friction coefficient of 0.42. The higher friction coefficient of the deposited layer is attributed to the harder microstructure, which resists adhesive transfer but is more susceptible to abrasive mechanisms. The presence of the hard beta-Mg17Al12 phase in the refined microstructure acts as an abrasive counter-body in the wear test, promoting three-body abrasion.

This wear behavior shift is significant for remanufacturing applications. In many industrial scenarios, such as automotive or military equipment, the dominant failure mode is abrasive wear rather than adhesive wear. The deposited layer's resistance to material loss through abrasion, despite its higher friction coefficient, represents a net improvement in service life for wear-critical components.

Engineering Practice and Remanufacturing Strategy

The study validates the feasibility of TIG welding as a remanufacturing technique for ZM5 magnesium alloy, providing data support for the repair of diverse damage types including surface wear, dimensional loss, and localized corrosion. For armor and military applications — the primary context of this research — the ability to restore worn surfaces on magnesium alloy components without complete part replacement offers substantial logistical and economic advantages.

In practice, the single-pass deposited layer offers the highest hardness but may have limited build-up capability. The multi-pass approach provides greater material deposition but with slightly lower hardness, likely due to interpass temperature effects that reduce the cooling rate. Engineers must balance these factors based on the specific repair requirement. The HAZ coarsening, while not detrimental to hardness, may affect the fatigue properties of the repaired component and should be considered in life assessment.

Study Insights and Reflections

This work is notable for its practical orientation toward remanufacturing rather than fundamental welding science. The finding that the deposited layer's wear mechanism shifts from adhesive to abrasive is a critical insight for engineers selecting remanufacturing processes. In many magnesium alloy applications, such as lightweight structural components in vehicles, the transition to abrasive wear dominance means that the repaired surface will exhibit different degradation patterns than the original material. This must be communicated to maintenance personnel so that service intervals and inspection criteria can be adjusted accordingly. The grain refinement achieved through TIG welding is a well-known phenomenon, but its quantification in the context of ZM5 alloy remanufacturing adds valuable data to the limited literature on magnesium alloy repair welding. For future work, the study suggests that investigating the effect of welding parameters on the volume fraction of the beta-Mg17Al12 phase, and potentially the use of flux-cored wires or consumable electrodes to further enhance the deposited layer properties, would be productive directions.