Continuous measurement by eddy current methods of age hardening in aluminum alloys

Abstract

Many materials processing operations such as age hardening heat treatments typically involve following predetermined time and temperature schedules to obtain the desired final material properties. The intelligent processing approach is to develop sensors for monitoring of material response to processing operation in real time. As an alloy age hardens its electrical resistivity changes. Hence, the process of aging can be monitored by measuring the change is resistivity relative to that of a non-age hardening material such as fully annealed aluminum. A device using two small, spiral-wound probes was designed to induce eddy currents within the pure aluminum and the aging alloy. The probes were incorporated as elements in an impedance bridge circuit. The bridge unbalance voltage decreased in value over time indicating decreasing relativity during the aging process. The monitoring concept was verified. Refinements such as improved impedance bridge circuitry and probe size/test frequency optimization are needed to unlock its full potential.