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Article

Improving the Properties of Laser-Welded Al–Zn–Mg–Cu Alloy Joints by Aging and Double-Sided Ultrasonic Impact Compound Treatment

School of Materials Science and Engineering, Inner Mongolia University of Technology, Hohhot 010051, China
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Author to whom correspondence should be addressed.
Academic Editors: Stefan Pogatscher and Peter J. Uggowitzer
Materials 2021, 14(11), 2742; https://doi.org/10.3390/ma14112742
Received: 27 April 2021 / Revised: 17 May 2021 / Accepted: 19 May 2021 / Published: 22 May 2021
(This article belongs to the Collection Alloy and Process Development of Light Metals)
To improve the loose structure and serious porosity of (Al–Zn–Mg–Cu) 7075 aluminum alloy laser-welded joints, aging treatment, double-sided ultrasonic impact treatment (DSUIT), and a combination of aging and DSUIT (A–DSUIT) were used to treat joints. In this experiment, the mechanism of A–DSUIT on the microstructure and properties of welded joints was analyzed. The microstructure of the welded joints was observed using optical microscopy, scanning electron microscopy, and electron backscatter diffraction (EBSD). The hardness and tensile properties of the welded components under the different processes were examined via Vickers hardness test and a universal tensile testing machine. The results showed that, after the aging treatment, the dendritic structure of the welded joints transformed into an equiaxed crystal structure. Moreover, the residual tensile stress generated in the welding process was weakened, and the hardness and tensile strength were significantly improved. After DSUIT, a plastic deformation layer of a certain thickness was generated from the surface downward, and the residual compressive stress was introduced to a certain depth of the joint. However, the weld zone unaffected by DSUIT still exhibited residual tensile stress. The inner microhardness of the joint surface improved; the impact surface hardness was the largest and gradually decreased inward to the weld zone base metal hardness, with a small improvement in the tensile strength. Compared with the single treatment process, the microstructural and mechanical properties of the welded joint after A–DSUIT were comprehensively improved. The microhardness and tensile strength of the welded joint reached 200 HV and 615 MPa, respectively, for an increase of 45.8% and 61.8%, respectively. Observation of the fractures of the tensile specimens under the different treatment processes showed that the fractures before the aging treatment were mainly ductile fractures while those after were mainly brittle fractures. After DSUIT of the welded joints, a clear and dense plastic deformation layer was observed in the fracture of the tensile specimens and effectively improved the tensile properties of the welded joints. Under the EBSD characterization, the larger the residual compressive stress near the ultrasonic impact surface, the smaller the grain diameter and misorientation angle, and the lower the texture strength. Finally, after A–DSUIT, the hardness and tensile properties improved the most. View Full-Text
Keywords: 7075 aluminum alloy; welded joint; aging; ultrasonic impact treatment; microstructure; EBSD; mechanical properties 7075 aluminum alloy; welded joint; aging; ultrasonic impact treatment; microstructure; EBSD; mechanical properties
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MDPI and ACS Style

Chen, F.; Liu, C. Improving the Properties of Laser-Welded Al–Zn–Mg–Cu Alloy Joints by Aging and Double-Sided Ultrasonic Impact Compound Treatment. Materials 2021, 14, 2742. https://doi.org/10.3390/ma14112742

AMA Style

Chen F, Liu C. Improving the Properties of Laser-Welded Al–Zn–Mg–Cu Alloy Joints by Aging and Double-Sided Ultrasonic Impact Compound Treatment. Materials. 2021; 14(11):2742. https://doi.org/10.3390/ma14112742

Chicago/Turabian Style

Chen, Furong, and Chenghao Liu. 2021. "Improving the Properties of Laser-Welded Al–Zn–Mg–Cu Alloy Joints by Aging and Double-Sided Ultrasonic Impact Compound Treatment" Materials 14, no. 11: 2742. https://doi.org/10.3390/ma14112742

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