Eddy Current at High Temperatures for in-Situ Control of Heat Treatment Precipitation in Hardening Aluminum Alloys

Abstract

Aluminum alloys are commonly used in commercial aircraft due to their low density and excellent mechanical properties. However, they need to become increasingly competitive in order that aluminum plate manufacturers maintaining market share. One way to ensure this is to improve or control parameters used in heat treatments. It is well known that electrical conductivity of metal alloys varies with microstructural change. Therefore, it is believed that In-Situ control of microstructural evolution can lead to optimization of treatment time, reduced energy consumption, increased production and final product quality, as well as reduction of costs, nonconformities and rework, having low implementation cost. In this way, eddy current sensors can be coupled to the furnace controller to optimize time and quality of heat treatment through the analysis of electrical conductivity with low implementation cost. Therefore, the objective of this work is to design, model and validate an eddy current sensor to monitor heat treatment of precipitation hardenable aluminum alloys in real time. Samples of 2024 alloy were prepared by solution treatment at 495 °C for 3 h and monitorization of aging treatment was performed at 190 °C for 9 h. Hardness, metallography, electrical conductivity (outside furnace) and relative electrical conductivity (inside furnace) were analyzed. The results were compared with the literature. There is a lot of discrepancy in the results of other authors. The eddy current sensor showed that behavior is similar to electrical conductivity through four-terminal method outside furnace.