Metallurgical Quality Control of Aged 7075 Al Alloy Using Eddy Current Nondestructive Testing Method

The eddy current non-destructive testing (ECT) is one of the electromagnetic methods that can be ‎used to evaluate and control the metallurgical quality of industrial alloys. The rapid implementation and digital nature of the answers have ‎led to its use in setting up automatic inspection and quality control lines . The purpose of this paper is to investigate the metallurgical quality control ‎conditions of 7075 aluminum alloy sheets after aging heat treatment ‎using the ECT method. For this purpose, the destructive tests of metallography, hardness and ‎electrical conductivity were performed along with the eddy currents non-destructive testing and ‎then their data were compared with each other. The sheet samples of this alloy were prepared in ‎the form of a 1.2 mm thickness. The solution heat treatment was performed at 470 centigrade ‎for 20 minutes and then artificial aging heat treatment was performed at different temperatures ‎and times. Microstructural studies were performed by optical and scanning electron ‎microscopes, standard conductivity (% ICAS) and Brinell hardness methods. Then, using a ‎eddy current apparatus at 8 kHz, the electromagnetic responses of the samples were evaluated ‎and compared. The results showed that to quality control and assurance of the aged products, ‎the use of hardness index alone can not suffice. In addition, the metallographic method has ‎executive limitations in production processes. It was found that the eddy current responses are ‎affected by microstructural changes resulting from aging process. Using this method, different ‎parts of 7075 aluminum alloy can be non-destructively separated from each other.‎