Si-bronze to 304 stainless steel GTA weld fusion zone

The use of fusion welding in joining both similar and dissimilar metals has been prevalent for many years. It is the same technique that has been used in joining stainless steels to copper and bronze metals. A proper welding procedure will result to joints with desired properties that can be used in vast range of applications in various fields such as fittings, water and gas systems, welding and repair of pipes and pumps among others.

Fusion welding for joining different materials is however affected greatly by the thermophysical and solid solubility properties of the materials to be joined which in most cases are very different such as the melting points. This has attracted studies aiminged at investigating different fusion welding techniques and consumables for joining of various copper alloys to stainless steels.

Researchers at Colorado School of Mines led by Professor Zhenzhen Yu investigated gas tungsten arc welds of Si-bronze and 304 stainless steel. They used two welding (filler) rods corresponding to the two base metals and thereafter drawn a comparison of the two processes. They further investigated the baseline welding parameter, impact of the filler metal on the mechanical properties and microstructure of the formed joints and characterizing the failure mechanisms that may occur in the dissimilar joints. This research work is currently published in the journal, Materials Science and Engineering A.

The choice of gas tungsten arc (GTA) welding process was because it is a very versatile and widely available welding technique. The authors commenced their study work by conducting mechanical tests on the two welds from the different filler metals using cross-weld tensile bars. In-depth analysis of the weld was done using various tools that included light optical microscopy among others. To analyze the model solidifications and stabilization of the different phases of the weld formation such as austenite, a thermodynamic software was used.

The authors obtained a reliable result from the of Si-Bronze filler welds. Mechanical properties such as the strength and ductility were observed to be higher than most of the reported values in the available literature for Cu-based to Fe-based weld joints.

The study by Professor Zhenzhen Yu and colleagues promotes the use of GTA in welding of dissimilar metals. It provides enough thermal energy and balance of forces that aids the formation of high-quality welds during the melting, mixing and solidification process. They also categorized copper-based fusion for a higher degree of hardness as they are capable of dispersing iron-based pools as compared to their counterpart Si-bronze base. GTAW with Si-bronze filler also aids formation of a very strong metallurgical bond because any fractures will always happen away from the fusion zone. It is also a protective measure for the fusion zone hence the formation of a high-quality weld.