Microstructural analyses of aluminum-magnesium-silicon alloys welded by pulsed Nd: YAG laser welding

• Published in: International journal of minerals, metallurgy and materials Vol. 27; no. 5; pp. 660 - 668
• Main Authors: Ebrahimzadeh, Hossain, Farhangi, Hassan, Mousavi, Seyed Ali Asghar Akbari, Ghahramani, Arman
• Format: Journal Article
• Language: English
• Published: Beijing University of Science and Technology Beijing 01.05.2020; Springer Nature B.V; School of Metallurgy and Materials Engineering,College of Engineering,University of Tehran,Tehran 11155-4563,Iran
• Subjects: Alloys; Aluminum; Aluminum base alloys; Base metal; Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Composites; Cooling; Cooling rate; Corrosion and Coatings; Cracks; Emission analysis; Field emission microscopy; Glass; Grain boundaries; Grain size; Heat treating; Heating; Hot cracks; Laser beam welding; Magnesium; Materials Science; Mesoscale phenomena; Metallic Materials; Metals; Microstructure; Natural Materials; Neodymium lasers; Optical microscopes; Particle size; Prediction models; Predictions; Pulsed lasers; Reagents; Scale models; Semiconductor lasers; Silicon; Solidification; Surfaces and Interfaces; Thin Films; Tribology; Vapor phases; Welding; YAG lasers; etching technique; inter-dendritic spacing; grain size; laser welding; hot crack formation model; aluminum-magnesium-silicon alloys
• ISSN: 1674-4799; 1869-103X
• DOI: 10.1007/s12613-020-2027-y

Revealing grains and very fine dendrites in a solidified weld metal of aluminum-magnesium-silicon alloys is difficult and thus, there is no evidence to validate the micro- and meso-scale physical models for hot cracks. In this research, the effect of preheating on the microstructure and hot crack creation in the pulsed laser welding of AA 6061 was investigated by an optical microscope and field emission electron microscopy. Etching was carried out in the gas phase using fresh Keller’s reagent for 600 s. The results showed that the grain size of the weld metal was proportional to the grain size of the base metal and was independent of the preheating temperature. Hot cracks passed the grain boundaries of the weld and the base metal. Lower solidification rates in the preheated samples led to coarser arm spacing; therefore, a lower cooling rate. Despite the results predicted by the micro and meso-scale models, lower cooling rates resulted in increased hot cracks. The cracks could grow in the weld metal after solidification; therefore, hot cracks were larger than predicted by the hot crack prediction models.