Study On Weld Shape In Electron Beam Welding Of High Strength Aluminum Alloy

The procedure of electron beam welding (EBW) of 20mm thick high strength Al-Cu alloy plate is investigated in this study. The properties of the joint and the factors that affect the properties are analyzed. The results show the weld shape is the main factor that affects the weld quality. Therefore, how to obtain good weld shape and evaluate the weld shape quality is the key in this study.The geometric models of the weld are given by analyzing the weld profile synthetically and then the geometric parameters are defined. Effect of the welding parameters on the geometric parameters is investigated and then the regularity of the weld shape is obtained. The results show that the nail-shape weld consists of two parts, namely nail-weld cap and nail-weld body. The form mechanism of the nail-weld cap is different from the nail-weld body. The shape of the nail-weld cap is only affected by the magnitude of the heat input but not the pattern of the heat input. The width of the nail-weld body has also the regularity mentioned above, however, the height is not only affected by the magnitude of the heat input but also the pattern of the heat input. A good weld shape can be obtained by adjusting the welding parameters according to the heat input and the melting efficiency.Images during electron beam welding of high strength Al-Cu alloy are acquired with the image sensing system. The characteristic parameters, such as W, LF and LR, are defined to describe the feature zone in the image and then the variation of the welding pool is investigated. The results show that the variation of the front part of the feature zone is different from that of the rear part. W or LF can describe the front part and LR describes the rear part. The variation of the characteristic parameters in fixed-point electron beam welding of 20mm thick high strength Al-Cu alloy is analyzed. The results show that the weld penetration depth is up to a stable magnitude in very short time. The subsequent increment of the weld penetration depth that is due to cumulative energy is smaller. W can reflect the weld penetration depth.The model describing the metal vapor recoiled from the keyhole is established with fluid mechanics analysis software Fluent. The variation of the feature zone on the keyhole in different weld penetration depth is investigated by numerical simulating. The width of the cross-section of the metal vapor in outlet is defined as the width of the metal vapor. As the diameter of the keyhole is equal to 0.5mm, the width of the metal vapor increases with increasing the weld penetration depth. The results coincide with the results in electron beam welding.Therefore, the variation of the feature zone in EBW has been analyzed by numerical simulating, which provides theoretical basis for subsequent analysis. While the weld penetration state is transforming from partial-penetration to full-penetration, W quickly decreases after slender increasing. W is processed with wavelet analysis and then the penetration information is identified. The results show the sharp pulse occurs secondly from the beginning of welding, which corresponds to the penetration state transforming from partial-penetration to full-penetration. So the task of identifying the penetration information is finished successfully. The visual program of wavelet analyzing the penetration information is programmed with Matlab.The results show that the appearance of weld can be described successfully by the variation coefficient of LR (VRL) and the variation coefficient of W (VW) as the characteristic parameters. The effect that the appearance of weld is described by both the characteristic parameters is the same. The function relationship between h and W is obtained by combining the image with the experimental weld penetration depth. The weld penetration depth h can be predicted by the function.A new method of predicting the weld profile is given by combining the image analysis with the combined model of nested heat source. On the non-destructive condition, h is obtained by analyzing image during welding and the distribution of the heat flux of the heat source is determined in advance, finally the more detailed weld profile can be obtained as long as the characteristic parameter of the image and the welding parameters are input. Electron beam welding of 20mm thick high strength Al-Cu alloy plate is carried out to realize the new method and validate it. The simulation results coincide with the experimental results, which validates the combined model of nested heat source and shows the new method is reliable.