Fabricating mixed material joints from Al-Cu using magnetic pulse welding

Melt based welding processes are indispensable to the modern manufacturing environment. In particular modern joining processes such as laser beam welding are the tools of choice when components have to be quickly welded with high joint quality. However, melt based processes face enormous difficulties when the welding partners are made from metals with substantially different properties, i.e. copper and aluminum. Unavoidable intermetallic phases form in the weld seams and may substantially limit their strength.

Thus the objective is to develop alternative industrial joining processes that form high strength mixed material joints without requiring a melted phase. A particular application requires mixed material joints involving cylindrical aluminum and copper parts.

Similar to explosion welding, it is possible to join nearly all metallic materials quasi melt-free using the so-called magnetic pulse welding (also known as electromagnetic pulse joining, EMP). The localized pressure pulse is generated without physical contact inside the part itself via a magnetic field pulse.

The technology is in particular known for applications in forming and connecting metal parts without any physical contact requirements. However, if the parameters are carefully chosen it is also possible to weld materials on an atomic scale.  It is especially critical to analyze the interface between the materials since it defines the ultimate strength of the joint.

IWS research aims at better understanding the process and subsequently at optimizing it for specific application requirements.

Mixed material joints from aluminum and copper were fabricated using EMP and then analyzed with respect to their properties. It was confirmed that the process is able to weld substantially different metals on an atomic scale. Metallographic analysis in combination with SEM/TEM investigations proved the existence of nanoscale intermetallic transition phases in interfaces that are otherwise apparently free of transition zones. Only seams thicker than 5 µm are critical in terms of crack formation.

The formation of intermetallic phases was strongly reduced through optimization of the process parameters resulting in a very high seam quality of the welded cylindrical parts.