Category Archives: Laser Welding

Effect of Laser Surface Melting on Corrosion Behavior of Aged Duplex Stainless Steel

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By: W.K. Chan, C.T. Kwok, K.H. Lo

Department of Electromechanical Engineering, University of Macau

Duplex stainless steels (DSSs), with a dual phase ferrite–austenite microstructure, have been widely used as the structural components for chemical industries, oil and gas production and offshore applications due to its outstanding corrosion resistance in chloride-containing environments. However, depletion of chromium and molybdenum is a well-known problem in DSSs, especially in welded assemblies, hot-worked and improperly heat-treated parts heated at temperatures ranging from 500 to 900°C. As the sigma phase forms, it depletes the neighboring regions of Cr and Mo, thereby lowering the Cr and Mo contents of the surface oxides over these regions. Then the DSSs become susceptible to corrosion attack. Laser surface melting (LSM) is a possible route to restore the corrosion resistance of DSSs by melting the surface with a laser beam followed by rapid solidification for homogenizing chemical compositions. Different laser parameters will cause different phase distributions in the DSSs, and hence various corrosion properties may be resulted. In present study, microstructure and corrosion behavior of aged DSS 7MoPlus (UNS S32950) were investigated in 3.5% NaCl solution at 25 oC before and after LSM. By LSM, the corrosion resistance of aged 7MoPlus was found to be significantly enhanced as reflected by the increase in the corrosion and pitting potentials and decrease in corrosion and passive current densities. The improvement in corrosion resistance of the aged 7MoPlus after LSM is mainly attributed to re-dissolution and removal of the s phase.

Remote Laser Welding of Zinc-Coated Sheetmetal Component in a Lap Configuration Utilizing Humping Effect

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By: Hongping Gu and Boris Shulkin

Stronach Centre for Innovation (SCFI)

With the advancement of high power fiber delivery lasers, remote laser welding becomes a reality and furthermore cost reduction on a new laser system in recent years drives adoption of laser welding process into production lines. Remote laser welding takes the advantages of less mechanical movement and better accessibility of the beam to the workpiece, thus much faster processing speed can be achieved. In most cases, remote laser welding involves lap welding. While the sheet metal components in automotive industry are mostly zinc coated for better corrosion resistance. One typical concern involved in laser lap welding of zinc coated materials is the potential porous weld caused by the zinc vapour. Since zinc has a vaporizing temperature that is lower than the melting point of steel, zinc vapour generated during laser welding will expel the molten metal out of the weld pool, resulting in rough weld. Therefore, laser beam lap welding of zinc coated steel components is not a straightforward process and it requires a special procedure to provide proper venting of the zinc vapour. Although there are several approaches to address this issue, many of the approaches are either impractical or too costly to apply to remote laser beam welding. Currently, the only practical solution for remote laser welding is to maintain a small gap between the joining materials. It has been proved through trials that a gap around 0.15 mm in size is optimum for such welding. The open question remains, however, how to generate such a small gap consistently and effectively at the welding location?

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Laser Welding of Micro-VLE-Measurement Device and its Practical Application

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By: Marika Hirvimäki, Heidi Piili, Arttu Jussila, Tuomas Purtonen, Matti Manninen, Petri
Uusi-Kyyny, Aarne Sundberg, Ville Alopaeus, Antti Salminen

Lappeenranta University of Technology, Finland
Aalto University, Department of Biotechnology and Chemical Technology, Finland
Machine Technology Centre Turku Ltd, Finland

The knowledge of phase equilibrium is critical for the modeling and operation of reactors and separation units. Vapor-liquid equilibrium (VLE) is defined as a state in which the component flux between the phases is equal in both directions. In the VLE-measurement the temperature, pressure and composition of both phases are determined for a range of concentrations. Typical volume of chemicals used in a VLE- measurement is 100 cm3 or above. When studying components that are either very expensive or hazardous the amount of chemicals used is preferably minimized. The other advantages of micro-VLE devices are e.g. small equipment size, surface area-to-volume ratio increases, which allows the unit to reach the temperature of the water faster and reduction of inside dimensions reduces the time required to reach equilibrium. In this study the volume of the measurement cell of micro-VLE was approximately 2.5 cm3.

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High-Brightness Disk Laser Welding of Magnesium Alloys

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By: Mohamed Wahba, Masami Mizutani, Yousuke Kawahito, Seiji Katayama

Central Metallurgical Research & Development Institute, Egypt
Graduate School of Engineering, Osaka University,  Japan
Joining and Welding Research Institute, Osaka University, Japan

Currently, the automotive industry is facing an increasing demand to increase fuel economy and reduce greenhouse gas emissions. Therefore, the trend is moving toward an increase in the percentage of components made of lightweight structural materials such as magnesium alloys. In order to implement these materials, it’s critical to have the ability to produce defect-free welds with reproducible high quality. Laser welding, owing to its versatile advantages, is very promising in this regard. Moreover, the recent development of fiber and disc laser sources with excellent beam quality has increased the capability and enhanced the performance of the laser welding process. Compared to Nd:YAG and CO2 laser sources, the superior beam quality can be utilized to obtain higher welding speeds, and deeper penetration, longer distance to the work piece and lower cost can be realized.

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Fiber Laser Blanking of Coil Strips at Extreme-Speed Extreme-Power

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By: Dr. Charles Caristan and Jay Finn

Air Liquide Industrial US LP, Automatic Feed Company

The blanking process consisting of cutting flat panels directly out of a metal coil is practiced in the automotive industry to the tune of 10 MM tons of steel coils processed each year for the North American market alone.  Up until now, CO2 laser-cutting technology is almost exclusively used to produce low-volume prototype blanks, whereas when it comes to high volume production, nearly 100% is still manufactured exclusively mechanically with shears and press die-blanking systems which hold high throughput and piece cost advantages.

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