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Yang S.,GM China Science Laboratory | Carlson And B.,General Motors | Kovacevic R.,Southern Methodist University
Welding Journal (Miami, Fla) | Year: 2011

It is a great challenge to laser weld zinc-coated steels in a gap-free lap joint configuration due to the formation of highly pressurized zinc vapor. In this study, different shielding conditions were designed to mitigate the highly pressurized zinc vapor. Argon, helium, the mixture of argon and carbon dioxide, and the mixture of argon and oxygen were selected as the shielding gases to study the effects of shielding conditions on weld quality. The introduction of a side shielding gas not only blew away the laser-induced plasma but also suppressed the instability of the molten pool caused by the highly pressurized zinc vapor. Under the optimal setting of shielding gas conditions, a stable keyhole was consistently formed that provided a channel to vent out the zinc vapor. Under this welding condition, the laser welding process was very stable. Consequently, a completely defect-free lap joint was achieved in a gapfree lap joint configuration. Experimental results demonstrated that this newly developed laser welding procedure was robust and cost effective, does not require preor postweld processing and can be directly applied in the industrial conditions. A high-speed CCD camera, assisted with a green laser as the illumination source, was used to monitor the behavior of the molten pool and the keyhole dynamics in real time. Energy-dispersive X-ray spectroscopy (EDS) experiments were carried out to analyze the chemical compositions in the welds. Furthermore, tensile shear tests and microhardness measurements were conducted to evaluate the mechanical properties of the welds. Source


Wang G.,Huazhong University of Science and Technology | Wang C.,Huazhong University of Science and Technology | Wang J.,Huazhong University of Science and Technology | Yang S.,GM China Science Laboratory | Hu X.,Huazhong University of Science and Technology
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2012

Defect of the porosity always occurs during laser welding of 5754 aluminum alloy and has a lot of bad influence on its mechanical property. Effects of the gap between two lap welding sheets on the porosity have been studied using fiber laser to weld 5754 aluminum alloy. It is found that setting a proper gap between two sheets can provide a passage for the escape of the porosity and decrease the porosity rate. When the gap changes from 0 to 0.2 mm, because of the capillary phenomenon, the escaping passage is closed by the solidification of the liquid weld metal, and the porosity decreases little. When the gap changes from 0.30 mm to 0.75 mm, the capillary phenomenon of the liquid weld metal between the gap weakens. So this part of weld metal is close to the fusion line and keeps liquid state. Then the escaping passage is opened and the porosity decreases obviously. It is also found that as the gap increases, the shear stress increases a lot. Source


Cao F.,University of Queensland | Shi Z.,University of Queensland | Song G.-L.,University of Queensland | Song G.-L.,Oak Ridge National Laboratory | And 3 more authors.
Corrosion Science | Year: 2015

The stress corrosion cracking (SCC) behaviour of solution heat-treated as-cast Mg0.1Zr, Mg1Mn, Mg0.1Sr, Mg0.3Si, Mg5Sn, Mg5Zn and Mg0.3Ca in distilled water (DW) was studied using the linearly increasing stress test (LIST). SCC susceptibility was related to the stress rate for all the Mg-X alloys except for Mg0.1Sr. At ~7.0×10-4MPas-1, Mg0.3Si and Mg5Sn were immune to SCC; Mg0.1Zr, Mg1Mn and Mg0.1Sr suffered medium SCC; Mg5Zn and Mg0.3Ca suffered relatively more serious SCC. At ~7.0×10-5MPas-1, Mg5Zn and Mg0.3Ca suffered the most serious transgranular SCC, whilst the other Mg-X alloys suffered medium SCC. © 2015 Elsevier Ltd. Source


Cao F.,University of Queensland | Shi Z.,University of Queensland | Song G.-L.,University of Queensland | Song G.-L.,Oak Ridge National Laboratory | And 3 more authors.
Corrosion Science | Year: 2015

The influence of hot rolling on the corrosion of Mg-X alloys (X=Gd, Ca, Al, Mn, Sn, Sr, Nd, La, Ce, Zr or Si) was investigated by immersion tests in 3.5% NaCl solution saturated with Mg(OH)2. The corrosion rates for all Mg-X alloys (except Mg0.1Zr and Mg0.3Si) decreased after hot rolling, attributed to fine-grained alloys having a more homogeneous microstructure, and fewer, smaller second-phase particles. For Mg0.1Zr and Mg0.3Si, the corrosion rate increased after hot rolling. There were a number of possible reasons, one of which was a greater sensitivity to the precipitation of deleterious Fe-rich particles. © 2014 Elsevier Ltd. Source


Cao F.,University of Queensland | Shi Z.,University of Queensland | Hofstetter J.,ETH Zurich | Uggowitzer P.J.,ETH Zurich | And 3 more authors.
Corrosion Science | Year: 2013

Corrosion was evaluated for ultra-high-purity magnesium (Mg) immersed in 3.5% NaCl solution saturated with Mg(OH)2. The intrinsic corrosion rate measured with weight loss, PW=0.25±0.07mmy-1, was slightly smaller than that for high-purity Mg. Some specimens had somewhat higher corrosion rates attributed to localised corrosion. The average corrosion rate measured from hydrogen evolution, PAH, was lower than that measured with weight loss, PW, attributed to dissolution of some hydrogen in the Mg specimen. The amount of dissolution under electrochemical control was a small amount of the total dissolution. A new hydride dissolution mechanism is suggested. © 2013 Elsevier Ltd. Source

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