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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.


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.


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) of hot-rolled Mg0.1Zr, Mg0.1Sr, Mg1Mn, Mg0.3Si, Mg5Sn, Mg0.7La, Mg0.9Ce, Mg0.6Nd, Mg6Al, Mg5Gd and Mg0.3Ca in distilled water (DW) was studied using the linearly increasing stress test (LIST). Hot-rolled Mg1Mn and Mg0.7La had some SCC susceptibility in DW. All the other hot-rolled Mg-X alloys had little SCC susceptibility in DW. There was no obvious difference of the fractography between the specimens tested in air and in DW. The increase of SCC resistance by hot-rolling was related to improvement of the microstructure. © 2015 Elsevier Ltd.


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.


Yang S.,GM China Science Laboratory | Wang J.,GM China Science Laboratory | Carlson B.E.,General Motors | Zhang J.,GM China Science Laboratory
Welding Journal | Year: 2013

Zinc-coated steels are increasingly used in the automotive industry due to their excellent corrosion resistance and long-term mechanical performance. However, it is still a great challenge to weld zinc-coated steels in a gap-free lap joint configuration. When zinc vaporizes at 906°C, which is much lower than the melting temperature of steel (1300°C), a high-pressure vapor will be generated at the faying interface of the steel sheets. If the zinc vapor is not appropriately vented out, a weld discontinuity such as porosity is usually produced in the weld and spatter is expelled from the weld. In this paper, a new laser welding process is proposed to join zinc-coated steels in a gap-free lap joint configuration. The new process uses a suction device to create a negative pressure zone (relative to ambient) directly above the molten pool. The purpose of this negative pressure zone is two-fold. First, a drag force is generated due to the external suction devicc, which can counterbalance the shear force induced by the erupting zinc vapor. Secondly, the negative pressure zone facilitates the zinc vapor to escape along the suction direction. As a result, the molten pool becomes more stable and the keyhole will remain open to allow the escape of zinc vapor. With vacuum assist, welds free of spatter and porosity can be obtained. In addition, mechanical properties of the welds are evaluated by tensile shear test and microhardness measurements.


Shi Z.,University of Queensland | Cao F.,University of Queensland | Song G.-L.,University of Queensland | Song G.-L.,Oak Ridge National Laboratory | And 2 more authors.
Corrosion Science | Year: 2013

Corrosion behaviour was characterised in salt spray and in 3.5% NaCl solution saturated with Mg(OH)2 of as-cast and solution heat-treated binary Mg-RE alloys. The corrosion rate in the immersion test for the solution heat-treated Mg-RE alloys was substantial, and was greater than that of high-purity Mg. These corrosion rates were probably caused by the particles in the microstructure and/or by Fe rich particles precipitated during the solution heat-treatment. The corrosion rate in the immersion tests for each as-cast Mg-RE alloy was greater than that of high-purity Mg, attributed to micro-galvanic acceleration caused by the second phase. Corrosion rates in salt spray had a general correlation with corrosion rates in the immersion tests, but there were differences. The values of apparent valence were always less than 2 consistent with Mg corrosion being only partly under electrochemical control. © 2013 Elsevier Ltd.


Cao F.,University of Queensland | Shi Z.,University of Queensland | Song G.-L.,University of Queensland | Song G.-L.,Oak Ridge National Laboratory | And 2 more authors.
Corrosion Science | Year: 2013

Corrosion of binary Mg-X alloys (as-cast and solution heat-treated) was characterised by immersion tests in 3.5% NaCl solution saturated with Mg(OH)2, and by salt spray. Alloys with high corrosion rates in immersion tests also had high corrosion rates in salt spray. Corrosion rates of the solution heat-treated alloys did not meet the expectation that they should be equal to or lower than those of high-purity Mg. There was circumstantial evidence that the higher corrosion rates were caused by the particles in the microstructure; the second phases had been dissolved. The corrosion rate of all alloys was faster than that of high-purity Mg. © 2013 Elsevier Ltd.


Wei C.,Huazhong University of Science and Technology | Zhang J.,GM China Science Laboratory | Yang S.,GM China Science Laboratory | Sun L.,GM China Science Laboratory | And 3 more authors.
Science and Technology of Welding and Joining | Year: 2015

A new laser welding process with the local cooling was presented and applied to two automotive dual phase steels, DP780 and DP980. The microstructure, microhardness, tensile properties of welded joints and limiting dome height (LDH) of welded blanks were investigated. It is observed that the local cooling during laser welding process can greatly reduce the martensite tempering and thus reduce the heat affected zone softening. The laser welded joints with the local cooling all failed at the base metal, and exhibit the comparable strength and ductility with the base metal. For the welded blanks with the local cooling, LDH is increased significantly, and failure initiates from the weld and propagates perpendicular to the weld. © 2015, Institute of Materials, Minerals and Mining.


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.


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.

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