Studying specifics of a permanent joint welding spot forming while the unit laser impulse effect on a low-carbon steel surface

Aeronautical and Space-Rocket Engineering

Design, construction and manufacturing of flying vehicles


DOI: 10.34759/vst-2020-3-94-102

Аuthors

Bakhmatov P. V.*, Pletnev N. O.**

Komsomolsk-on-Amur State University (KnASU), 27, Lenin str., Komsomolsk-on-Amur, 681013, Russia

*e-mail: mim@knastu.ru
**e-mail: nik1111ta@mail.ru

Abstract

Laser welding technology application in the aerospace industry will significantly reduce the weight of the aircraft structure, material consumption and production time for parts and accessory manufacturing.

The thermal cycle of laser welding ensures minimum time of the area staying in the overheated state, eliminating thereby the possibility of grain growth and mechanical properties reduction of steels.

The article presents the studies of structural changes in the weld metal obtained by the unity effect of laser radiation on the steel surface.

The performed microstructural analysis allows establishing the weld metal formation staging, and its components, including the microhardness defining in each particular zone, which contributes to understanding and predicting the behavior of the weld metal while parts or structures operation.

The three most pronounced zones were defined while the unit laser impulse effect. They are:

1 – the arc-like zone of the dendrite structure.

2 – the recrystallization zone, located symmetrically to the zone 1. The structure of this zone is distributed randomly, the tempering bainite mainly prevails.

3 – the tempered perlite zone with uniformly sized grains of an average diameter of 40–70 microns. Zone 3 adjoins zone 2 and the welding spot surface.

One more zone with extremely insignificantly distorted structure of the basic metal is being observed under the weld-fusion line towards the basic metal.

Analysis of the average area of the zones revealed the following: zone 1 has a predominant area of 51.2% of the total weld metal area, and 47.5% along the computed volume.

High crystallization rates contribute to the dendritic structure development of zone 1, and the heat-affected heating zone therewith contributes to the uniform tempering of zones 2 and 3 and formation ofstructures of bainite and tempering sorbite respectively.

It was established as well that in the process of exposure, temperature conditions are being created for recrystallization and tempering of quenching structures. Thus, to ensure equal strength of the welded joint with the base metal, it is necessary to recommend tempering to relieve residual stresses and partial recrystallization of zone 2 even for low carbon steels.

Keywords:

permanent joints, laser welding, laser impulse, welding of low-carbon steels, precision laser welding of aviation products, pulsed solid-state laser, structural changes in the weld metal

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