Characterization of AZ31B magnesium alloy joints welded with a Nd:YAG laser

Abstract

In the present study, an AZ31B magnesium alloy was welded using a low-power pulsed Nd:YAG laser attached to a six-axis welding robot. The welding metallurgical characteristics, including microstructure, porosity formation, texture evolution and microhardness distribution were systematically investigated using a scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and a microhardness tester. The transverse cross-sectional microstructure of the AZ31B-alloy joint was composed of the base metal (BM), columnar-grain zone (CGZ) and equiaxed-grain zone (EGZ) in the center of the fusion zone (FZ). Some pores were observed in the FZ and believed to be related to the pre-existing pores in the BM. Especially, it was noted that many columnar grains observed in the transverse cross-section of the FZ were almost perpendicular to the solid-fusion boundary. Nevertheless, a large number of fine equiaxed grains formed on the top surface of the FZ and exhibited obvious random orientations. Different grain-growth mechanisms found on the transverse cross-section and the top surface of the weld bead were empirically investigated. Owing to apparent grain coarsening, the lowest microhardness value (~43 HV) was detected in the center of the FZ, which was evidently lower than that of the BM (~68 HV). Keywords: AZ31B magnesium alloy, Nd:YAG laser welding, microstructure, pores, texture, electron backscatter diffraction Avtorji {tudije so magnezijevo zlitino AZ31B varili s pulznim Nd:YAG laserjem nizke mo~i, name{~enem na {estosnem varilnem robotu. Sistemati~no so izvedli metalur{ko karakterizacijo varjenja, vklju~no z analizo mikrostrukture, analizo tvorbe poroznosti in razvoja teksture s pomo~jo vrsti~ne elektronske mikroskopije (SEM) v kombinaciji s sipanjem povratnih elektronov (EBSD). Porazdelitev mikrotrdote po preseku zvara so dolo~ili z merilnikom mikrotrdote. Posnetki mikrostrukture v pre~nem preseku zvarnega spoja zlitine AZ31B so pokazali, da je le ta sestavljen iz osnovne kovine (BM; angl.: base metal), cone stebri~astih kristalnih zrn (CGZ; angl.: columnar grains zone), cone enakoosnih zrn (EGZ; angl.: equiaxed grains zone) in centralne staljene cone (FZ, angl.: fusion zone). V FZ so opazili tudi nekaj por in avtorji verjamejo, da je to posledica predhodno obstoje~ih por v BM. [e posebej poudarjajo opa`anje, da se mnoga stebri~asta zrna nahajajo v pre~nem preseku FZ , ki so skoraj pravokotna na fazno mejo trdno-talina. Kakorkoli, na vrhu povr{ine FZ se nahaja veliko {tevilo tvorjenih drobnih enakoosnih kristalnih zrn z o~itno naklju~no orientacijo. Avtorji prispevka empiri~no razpravljajo v~lanku tudi o razli~nih mehanizmih rasti zrn med pre~nim presekom in vrhom povr{ine varilne posteljice (bazen~ka staljene kovine). Zaradi jasne rasti zrn so najmanj{o mikrotrdoto (~43 HV) izmerili v centru FZ, kar je o~itno precej manj kot v BM (~68 HV). Klju~ne besede: magnezijeva zlitina AZ31B, varjenje z Nd:YAG (Neodim:Itrij-Aluminijev granat) laserjem, mikrostrukture, pore, teksture, sipanje povratnih elektronov

Research on mapping recognition of arc welding molten pool characterisation and penetration state based on embedded system

“…In the past 10 years, with the rapid development of computer vision technology, it has become an important research to obtain the geometric shape information related to the molten pool through the processing of visual images to reflect the dynamic changes of the welding process penetration, and to realise the real-time control of the weld penetration. Direction [6]. In certain welding site environments that are not suitable for manual operations or when manual vision cannot meet the requirements, visual sensor systems are often used instead of manual labour; on the other hand, for the production process of large quantities of industrial products, due to human subjective reasons, it is often caused The efficiency and accuracy of manual visual inspection of product quality is low, and the visual sensor system can improve the production efficiency and the degree of automation of the welding process [7].…”