Resistance spot welding of AZ series magnesium alloys: Effects of aluminum content on microstructure and mechanical properties

Abstract The microstructural evolution of the spot welded AZ31, AZ61 and AZ80 magnesium alloys was studied via optical and scanning electron microscopy. As the Al content of the magnesium base alloy increased from 3 wt% (AZ31) to 6% (AZ61) and 8% (AZ80), columnar to equi-axed dendrite transition and grain refinement in the fusion zone were enhanced. However, the increasing amount of the β-Mg17(Al,Zn)12 phase in the heat affected zone (HAZ) and fusion zone (FZ) resulted in the reduction of the tensile shear strengths of the AZ61 and AZ80 welds compared to those of AZ31 welds. Moreover, in the tensile-shear testing, the AZ61 and AZ80 welds failed in the heat affected zone along the fusion boundary, because micro-cracking occurred preferentially at the interfaces between β particles and Mg matrix. Post-weld solutionizing treatment was found to significantly reduce the quantity of β particles in heat affected and fusion zones of AZ61 and AZ80 welds. This led to an increase in the weld strengths of AZ61 and AZ80 alloys because the heat treatment eliminated the β particles and cracks propagated into the coarse-grained heat affected zone and then base material. For the heat treated welds, grain size was found as a major factor in the failure mode.

[1]  A. Ohmori,et al.  Optimisation of welding using two Nd–YAG laser beams combined at workpiece surface , 2000 .

[2]  J. A. Pask,et al.  Wetting under chemical equilibrium and nonequilibrium conditions , 1974 .

[3]  H. I. Laukli,et al.  Divorced eutectic in a HPDC magnesium–aluminum alloy , 2004 .

[4]  M. Ohno,et al.  Thermodynamic assessment of Mg–Al–Mn phase equilibria, focusing on Mg-rich alloys , 2005 .

[5]  Tadanobu Inoue,et al.  Deformation mechanism near crack-tip by finite element analysis and microstructure observation in magnesium alloys , 2010 .

[6]  L. Zhen,et al.  Effects of precipitates on fatigue crack growth rate of AA 7055 aluminum alloy , 2010 .

[7]  Shicheng Zhang,et al.  Fracture mechanics solutions to spot welds , 2001 .

[8]  Z. Chen,et al.  Effect of cooling conditions during casting on fraction of β-Mg17Al12 in Mg–9Al–1Zn cast alloy , 2010 .

[9]  Chuen-Guang Chao,et al.  Characterization on electron beam welds and parameters for AZ31B-F extrusive plates , 2007 .

[10]  R. Reed-hill,et al.  Additional modes of deformation twinning in magnesium , 1957 .

[11]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[12]  A. Zarei‐Hanzaki,et al.  An investigation into the hot ductility behavior of AZ81 magnesium alloy , 2012 .

[13]  D. Potter.  The structure, morphology and orientation relationship of V3N in α-vanadium , 1973 .

[14]  장윤희,et al.  Y. , 2003, Industrial and Labor Relations Terms.

[15]  H. Somekawa,et al.  Effect of grain refinement on fracture toughness in extruded pure magnesium , 2005 .

[16]  N. Zhou,et al.  Effects of Heat Treatment on Grain-Boundary β-Mg17Al12 and Fracture Properties of Resistance Spot-Welded AZ80 Mg Alloy , 2013, Metallurgical and Materials Transactions A.

[17]  Mingxing Zhang,et al.  Crystallography of Mg17Al12 precipitates in AZ91D alloy , 2003 .

[18]  D. Qiu,et al.  Identifying close-packed planes in complex crystal structures , 2010 .

[19]  H. Somekawa,et al.  Effect of texture on fracture toughness in extruded AZ31 magnesium alloy , 2005 .

[20]  Gunnar Eriksson,et al.  FactSage thermochemical software and databases - recent developments , 2009 .

[21]  Zemin Wang,et al.  Characterization of AZ31B wrought magnesium alloy joints welded by high power fiber laser , 2011 .

[22]  C. Bulle-lieuwma,et al.  Novel scheme for the preparation of transmission electron microscopy specimens with a focused ion beam , 1993 .

[23]  Y. Zhou,et al.  Microstructure Refinement After the Addition of Titanium Particles in AZ31 Magnesium Alloy Resistance Spot Welds , 2012, Metallurgical and Materials Transactions A.

[24]  S. Guldberg,et al.  Microstructure and crystallographic orientation relationship in directionally solidified Mg–Mg17Al12-eutectic , 2000 .

[25]  Margaret Nichols.  Trans , 2015, De-centering queer theory.

[26]  Xiaoling Xiao,et al.  Characterisation of precipitate phases in magnesium alloys using electron microdiffraction , 2001 .

[27]  L. P. Pook,et al.  Fracture mechanics analysis of the fatigue behaviour of spot welds , 1975 .

[28]  New-Jin Ho,et al.  Electron-beam welding behavior in Mg-Al-based alloys , 2002 .

[29]  Pierre Villars,et al.  Pearson's handbook of crystallographic data for intermetallic phases , 1985 .

[30]  Z. Fan,et al.  A new heat treatment procedure for rheo-diecast AZ91D magnesium alloy , 2006 .

[31]  Zhen-hua Chen,et al.  CO2 laser beam welding of dissimilar magnesium-based alloys , 2008 .

[32]  H. Somekawa,et al.  Fracture toughness in Mg–Al–Zn alloy processed by equal-channel-angular extrusion , 2006 .

[33]  S. Bhole,et al.  Microstructure and tensile properties of thixomolded magnesium alloys , 2010 .

[34]  B. Radhakrishnan,et al.  Kinetics of grain growth in the weld heat-affected zone of alloy 718 , 1993, Metallurgical and Materials Transactions A.

[35]  J. Feng,et al.  Nugget growth characteristic for AZ31B magnesium alloy during resistance spot welding , 2006 .

[36]  P. Čížek,et al.  Characteristics of the contraction twins formed close to the fracture surface in Mg–3Al–1Zn alloy deformed in tension , 2008 .

[37]  Marc A. Meyers,et al.  THE ONSET OF TWINNING IN METALS: A CONSTITUTIVE DESCRIPTION , 2001 .

[38]  Shicheng Zhang,et al.  Stress Intensities at Spot Welds , 1997 .

[39]  C. Chao,et al.  Aluminum element effect for electron beam welding of similar and dissimilar magnesium–aluminum–zinc alloys , 2007 .

[40]  G. Shiflet,et al.  The role of structural ledges as misfit- compensating defects: fcc-bcc interphase boundaries , 1994 .

[41]  Y. Zhou,et al.  Bonding of immiscible Mg and Fe via a nanoscale Fe2Al5 transition layer , 2011 .

[42]  Sunghak Lee,et al.  In situ fracture observation and fracture toughness analysis of squeeze cast AZ51–xSn magnesium alloys , 2010 .

[43]  D. Ando,et al.  Roles of deformation twinning and dislocation slip in the fatigue failure mechanism of AZ31 Mg alloys , 2010 .

[44]  M. Yoo.  Slip, twinning, and fracture in hexagonal close-packed metals , 1981 .

[45]  H. Wondratschek,et al.  International Tables for Crystallography, Volume A1 , 2005 .

[46]  Y. Zhou,et al.  The Mechanisms of Resistance Spot Welding of Magnesium to Steel , 2010 .

[47]  D. Ando,et al.  Relationship between deformation twinning and surface step formation in AZ31 magnesium alloys , 2010 .

[48]  R. Pandey,et al.  Effect of aging treatments on the kinetics of fatigue crack growth in 7010 aluminum alloy , 2006 .

[49]  D. Stefanescu.  Fundamentals of Solidification , 2004 .

[50]  Y. Zhou,et al.  Resistance-Spot-Welded AZ31 Magnesium Alloys: Part I. Dependence of Fusion Zone Microstructures on Second-Phase Particles , 2010 .

[51]  D. L. Chen,et al.  Resistance spot weld fatigue behavior and dislocation substructures in two different heats of AZ31 magnesium alloy , 2011 .