Published online by Cambridge University Press: 15 February 2011
The U.S. Bureau of Mines has studied the capacitive discharge weld interface between Al and Fe using optical and transmission electron microscopy (TEM). Capacitive discharge welding (CDW) is a rapid solidification process in which the amount of molten metal at the interface is small compared to the sample size. As a result, high cooling rates (106 K/s) can be achieved, providing a weldment made up of small grains. Large magnetic fields produced by the process tend to mix the molten metals at the interface to form a complex alloy, the nature of which depends upon the starting electrode materials. This effect is characterized by a marblecake pattern in optical micrographs. The amount of mixing is related to the melting temperature of the cathode with respect to the anode. Increased mixing occurs when the melting temperature of the cathode is higher than the melting temperature of the anode. TEM has revealed that when aluminum is the anode material, the iron grains of the cathode are surrounded by a layer of aluminum. When the iron is the anode, a thin layer of iron surrounds the aluminum grains.