Nonvel Nondestructive Evaluation Techniques for Intertia-Friction Welds in a SiC-Reinforced High-Temperature Aluminum Alloy
The feasibility of different NDE techniques for evaluating the microstructural characteristics of the heat- and deformation zone (HDZ) of inertia-friction welds produced in a high-temperature discontinuously-reinforced aluminum (DRA) alloy has been investigated. High-temperature DRA composites have been developed for elevated-temperature application in the aerospace industry by incorporating SiC particulate reinforcement into a rapidly-solidified aluminum alloy [1,2]. The DRA composite used in this study was dispersoid-strengthened 8009/SiC/11p made by Allied-Signal Co. The specimens were first cut into 1″-diameter rods from larger extruded billets. These rods were then inertia-friction welded at different axial forces ranging from 89 kN to 156 kN at 5,000 rpm. Generally, the dynamic flow experienced by the outer and inner HDZ microstructures during the welding process greatly affects weld quality (tensile strength, fracture toughness, fatigue strength, etc.). Ultrasonic evaluation of the characteristic shape and size of the HDZ has been previously showed to yield valuable information on inertia-friction welds of aluminum, steel, and copper [3,4]. Similar methods can be readily adapted to the inspections of high-temperature DRA composite welds, too. In addition, the orientation and density of the flow lines at different distances from the interface can be evaluated to reconstruct the formation of the weld. In most cases, flow lines can be visualized only by selectively etching the polished surfaces of metallurgical samples. Because of the usually very weak ultrasonic contrast presented by such flow lines they cannot be nondestructively detected let alone mapped. We shall demonstrate that the discontinuous nature of the silicon carbide reinforcement allows the particulates to align themselves with the local direction of plastic flow during weld formation, thereby presenting an excellent contrast mechanism for ultrasonic mapping of the flow pattern in the HDZ.