Interdependence of Hydrogen and Microporosity in Magnesium Alloy AZ91

Mikucki, Barry A.; Shearouse, James D.

doi:10.4271/930754

Cited by 20 publications

(22 citation statements)

References 2 publications

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“…However, many tiny pin holes still existed although hydrogen content was reduced. It is in accord to the result of the literature, 10 which indicated that at gas content below the maximum solid solubility, the amount of microporosity was directly proportional to the hydrogen content of AZ91 alloy melts. Figure 4 shows the structure of microporosity in AZ91 alloy specimen, which melted under flux protectionzdegassed with Ar gas.…”

Section: Effect Of Hydrogen Content On Structure Of Microporositysupporting

confidence: 92%

“…A recent work that employed a new hydrogen measurement instrument confirmed that even if gas concentration was below the maximum solid solubility, the amount of microporosity in castings was directly proportional to the hydrogen content of Mg alloy melt. 10 However, there are very few references available about the quantitive measurement of hydrogen content in Mg alloy melt and the relation of mechanical property with microporosity. This paper measured hydrogen levels in Mg alloy melt under different conditions.…”

Section: Introductionmentioning

confidence: 99%

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Influence of hydrogen levels on porosity and mechanical properties of Mg alloy castings

Wu¹,

Song²,

Fukuda³

et al. 2008

International Journal of Cast Metals Research

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The effects of hydrogen levels on microstructure of porosity and mechanical properties of magnesium alloy castings were investigated. The hydrogen content of AZ91 alloy melt under ArzHFC-134a mixed gas protection was 103 cm 3 kg 21 , which was less than that of 139 cm 3 kg 21 under flux protection, therefore the effect of gas protection was better. The porosity ratio in microstructure of castings melted under gas protection was 1?8%, which was also less than that of 2?6% under flux protection. The hydrogen content of melt under flux protection and degassed with Ar gas was 70 cm 3 kg 21 , and the corresponding porosity ratio in microstructure of castings was only 0?6%. The density of the samples was increased with decreasing hydrogen content. The tensile strength of AZ91 alloy casting sample under flux protection and degassed with Ar gas was 21% higher than that of undegassed one, and the elongation was also 50% higher.

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Section: Effect Of Hydrogen Content On Structure Of Microporositysupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Influence of hydrogen levels on porosity and mechanical properties of Mg alloy castings

Wu¹,

Song²,

Fukuda³

et al. 2008

International Journal of Cast Metals Research

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“…A. Mikucki [4] have suggested that the hydrogen solubility of pure magnesium is 29 ppm and that the micropores may not be formed by the gas evolution mechanism below this hydrogen solubility. Also, in their sequential study, they have reported that the maximum hydrogen solubility of AZ91D alloy is 24 ppm, and the solubility limit of liquid phase and Mg 17 Al 12 phase is 7.7 ppm and 2.3 ppm, respectively at eutectic temperature [5]. This means that there is a possibility that the hydrogen solubility limit of each phase will be lowered by the increase in Alconcentration.…”

Section: Formation Of Micropores On Solidification Of As-cast Magnesimentioning

confidence: 97%

“…To date, many studies on the formation of micropores in as-cast Mg-alloy have been conducted [2,3]. Recently, since experimental results on the hydrogen solubility limit of individual micro-components have been reported [4,5], detailed discussion on the formation mechanism of micropores and its effect on mechanical properties is all the more practicable. Research on the mechanical properties of Mg-based alloy have trended to report on the effect of the alloy element [6][7][8] and grain size [9].…”

Section: Introductionmentioning

confidence: 99%

Effect of microporosity on tensile properties of as-cast AZ91D magnesium alloy

Lee¹

2002

Met. Mater. Int.

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In the present study, the effect of microporosity on the tensile properties of as-cast AZ91D magnesium alloy was investigated through experimental observation and numerical prediction. The test specimens were fabricated by die-casting and gravity-casting. For gravity-casting, the inoculation and use of various metallic moulds were applied to obtain a wide range of microporosity. The deficiency of the interdendritic feeding of the liquid phase acted as a dominant mechanism on the formation of the micropores in the Mg-Al-alloys, rather than the evolution of hydrogen gas. Although tensile strength and elongation has a nonlinear and very intensive dependence upon microporosity, the yield strength appeared to have a linear relationship with microporosity. However, it was possible to quantitatively estimate the linear contribution of microporosity on the individual tensile property for a range of microporosity, which was below about 1%. The numerical prediction suggests that the effect of microporosity on fractured strength and elongation decreased as the strain hardening exponent increased. Furthermore, the shape and distribution of micropores may play a more dominant role than local plastic deformation on the tensile behavior of AZ91D alloy.

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“…One of the main issues is pore formation that affects the mechanical properties of the weld. There are different mechanisms that cause pore formation in the laser welding process such as hydrogen pores [1,3], unstable keyhole [4], pre-existing pores, surface coating [1,5], gas entrapment [1,6], and alloy elements with a low vaporization point [7].…”

Section: Introductionmentioning

confidence: 99%

Effect of process parameters on the weld quality in laser welding of AZ31B magnesium alloy in lap joint configuration

Harooni¹,

Carlson²,

Kovacevic³

2013

International Congress on Applications of Lasers &Amp; Electro-Optics

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Magnesium is the lightest structural metal; therefore it has been used in a variety of industries such as automotive, aerospace, electronics and defense. Among different joining processes, laser welding is advantageous due to its low heat input, high depth-towidth weld ratio and good mechanical properties. In this study, a fiber laser is used to weld AZ31B magnesium alloy in a lap joint configuration. Pores were formed in the weld bead that are caused by a thick oxide layer existing on the surface of asreceived AZ31B samples. Process parameters including laser power and welding speed are studied to determine their effects on pore formation and maximum lap-shear load of the weld bead. Hardness and tensile tests are carried out to reveal the mechanical properties of the weld bead. A regression analysis is performed that establishes a mathematical relation between the process parameters and the weld maximum lap-shear load. Three regression models are compared in order to determine their accuracy in prediction of the maximum lap-shear load and results revealed that the linear model could best predict the maximum lap-shear load by process parameters.

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Interdependence of Hydrogen and Microporosity in Magnesium Alloy AZ91

Cited by 20 publications

References 2 publications

Influence of hydrogen levels on porosity and mechanical properties of Mg alloy castings

Influence of hydrogen levels on porosity and mechanical properties of Mg alloy castings

Effect of microporosity on tensile properties of as-cast AZ91D magnesium alloy

Effect of process parameters on the weld quality in laser welding of AZ31B magnesium alloy in lap joint configuration

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