Mechanical and Metallurgical Investigation of AISI 304 Stainless Steel and Commercially Pure Copper Dissimilar Metal Couple Weldments

Abstract

In recent years, the complex equipment/systems require a variety of materials with contradictory properties to improve performance and to reduce cost. This has resulted in increased demands for techniques to weld dissimilar materials and for use in large scale industrial production. Particularly the joining of AISI 304 stainless steel and commercially pure copper dissimilar metal couple is extensively employed for various industrial applications, i.e., in the field of electrical and electronics, cryogenics, power generation and transmission, food processing plants, neutron absorbent coolant system, automotive turbo compressor fan and shaft joints, etc. The main purpose of this combination is to utilize the high strength of the steel and high electrical conductivity of copper simultaneously with significant corrosion resistance.
The objectives of the present research work are to characterize and determine the weldability of AISI 304 SS and CP copper dissimilar metal couples without use of any kind of filler materials based on experimental, numerical simulation and statistical modeling approaches. The investigations are carried out by three different types of fusion welding processes such as continuous wave CO2 laser, pulsed wave TIG arc and pulsed wave Nd:YAG laser. The experimental work aimed to investigate the welding induces microstructure, microhardness, residual stress, compositional analysis and tensile properties of butt joint of SS-Cu weldments under different welding conditions separately. The numerical simulation (using ANSYS 15.0 FLUENT® environment) including weld pool shape and temperature obtained during welding have been investigated for laser welding and validate with the experimental results. The aim of statistical modeling is to predict and optimize the SS-Cu weldments in industrial application through desired weld structure with proper microstructure and minimum defects. The design of experiments (DOE) approaches are implemented to design the experiments, develop mathematical models and optimize the welding operations with proper parametric settings.
Although joining of dissimilar metals is a tough task due to their mismatch in properties like physical, chemical thermal, etc., the experimental results showed that a successful weldment of SS-Cu butt joint has been achieved by all three welding processes. The HAZ in CO2 laser welded specimens are found minimum i.e. 10 μm compared to other welding processes, and it is narrower for SS side in comparison to Cu side. The microhardness in the weld zone found to be more than the base materials. The numerical simulation results shows a good agreement with the experimental results in terms of shape of the weld pool and temperature profile for CO2 laser and Nd:YAG laser respectively. A greater fitness of the Taguchi orthogonal array design model for all welding processes, confirms from the corresponding ANOVA table, probability and residual plots. In pulsed TIG arc welding, the formation of weld craters at the end of the weld is resolved by varying ramp down time experimentally. Welding approaches like proper selection of input process parameters and preheating of welding specimens are successfully applied for improvement of weld strength as well as penetration depth during pulsed wave Nd:YAG laser welding processes.