Analysis of the Process Parameters, Post-Weld Heat Treatment and Peening Effects on Microstructure and Mechanical Performance of Ti–Al Dissimilar Laser Weldings

Abstract

Dissimilar Ti–Al laser weldings are very interesting due to their difficulties in being processed because of the different physical properties of the alloys and the crack formations during cooling and solidification. In this study, the effect of laser offset and defocusing on microstructure, geometry and mechanical properties response of 2 mm thick dissimilar AA6061/Ti-6Al-4V laser welds was analyzed. Moreover, in order to reduce residual stresses, the joints were both heat-treated and mechanically treated by ultrasonic peening. The welds microstructure was found to be martensitic in the Ti-6Al-4V fusion zone, columnar dendritic in the AA6061 fusion zone and partially martensitic in the Ti-6Al-4V heat-affected zone. Intermetallic compounds based on the Al–Ti system were detected at the AA6061/Ti-6Al-4V interface and in the aluminum fusion zone. Both negative defocusing and higher laser offset improved the tensile performance of the welds, mainly by reducing the amount of brittle intermetallic compounds. The stress relaxation heat treatment, leading to the aging of the martensite and the increasing of the size of the intermetallic compound, reduced the tensile strength and ductility of the joints. On the contrary, for dissimilar Al–Ti welds, mechanical treatment was effective in increasing joints ductility and, moreover, corrosion resistance.

A Review: Laser Welding of Dissimilar Materials (Al/Fe, Al/Ti, Al/Cu)—Methods and Techniques, Microstructure and Properties

“…Katayama et al [ 108 ] continued research [ 17 ] on high-speed laser welding of titanium and aluminum (50 m/min) using a high-speed camera, and a more detailed study using in-situ spectroscopic analysis of plume induced during Al (upper)–Ti (lower) and Ti (upper)–Al (lower) dissimilar welding. Casalino G. et al [ 110 ] continue their studies [ 62 ] in this case, in addition to the offset of the laser beam, “-” defocusing, heat treatment, and ultrasonic peening are used. This allows obtaining the mechanical properties of the joint at the level of 173 MPa and the elongation of 4.5%.…”

Advances in Laser Materials Processing

“…The post-processing (mechanical, heat and plasma treatment) of laser welds and parts produced by laser additive manufacturing [17][18][19].…”

“…The effect of laser offset and defocusing on microstructure, geometry, and mechanical property responses of 2 mm-thick dissimilar AA6061/Ti-6Al-4V laser welds were studied in [17]. In order to reduce residual stresses, the joints were both stress relaxation heattreated (at 530 • C for 2 h followed by air cooling) and mechanically treated by ultrasonic peening (for 1 min/side, the diameter of the peening needle was 3 mm, and the vibration frequency was 20 kHz).…”

Effect of Preheating and Post-Heating on the Microstructures and Mechanical Properties of TC17-Ti2AlNb Joint with Electron Beam Welding

“…Studies have shown that an excessive temperature gradient during Ti 2 AlNb alloy welding was prone to cracking and welding defects [11]. Because of the high residual stress during the heat treatment process after welding, the secondary crack will also appear further [12,13]. The mechanical properties of the welded joints between different materials are anticipated to improve thanks to the excellent weldability of TC17 titanium alloy [14,15].…”