Observations on the Mechanisms of High Resistance Junction Formation in Aluminum Wire Connections

The basic mechanism of high resistance junction formation in duplex connectors wired with aluminum was investigated. Laboratory experiments to simulate loose connections were made both in actual duplex connectors and in an experimental apparatus. Microstructural observations were made by scanning electron microscopy and x-ray microanalysis of the structures formed at the interfaces between the circuit components during high resistance junction formation. At the iron screw/aluminum wire interface, the arcing process which occurs in a loose connection causes high temperatures in excess of 1500 °C and material transport between the components. Under these conditions, aluminum and iron react to form intermetallic compounds such as Fe₃Al and FeAl₃. The formation of an extensive zone of these compounds adjacent to the iron-aluminum interface in duplex connectors was revealed by electron metallography. In duplex connectors tested to glow failure, the formation of intermetallic compounds such as CuAl₂ and Cu₂ZnAl was observed at the brass plate/aluminum wire interface. These intermetallic compounds have a resistivity of the order of 100 × 10^-6 ohm-cm or higher which may provide sufficient resistence at the current-carrying interface to lead to significant I ² R heating losses at the interface.