مقاله جوشکاری با عنوان :

Resistance-Spot-Welded AZ31 Magnesium Alloys:
Part I. Dependence of Fusion Zone Microstructures
on Second-Phase Particles
L. XIAO, L. LIU, Y. ZHOU, and S. ESMAEILI

چکیده:

A comparison of microstructural features in resistance spot welds of two AZ31 magnesium
(Mg) alloys, AZ31-SA (from supplier A) and AZ31-SB (from supplier B), with the same sheet
thickness and welding conditions, was performed via optical microscopy, scanning electron
microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM).
These alloys have similar chemical composition but different sizes of second-phase particles due
to manufacturing process differences. Both columnar and equiaxed dendritic structures were
observed in the weld fusion zones of these AZ31 SA and SB alloys. However, columnar dendritic
grains were well developed and the width of the columnar dendritic zone (CDZ) was much
larger in the SB alloy. In contrast, columnar grains were restricted within narrow strip regions,
and equiaxed grains were promoted in the SA alloy. Microstructural examination showed that
the as-received Mg alloys contained two sizes of Al8Mn5 second-phase particles. Submicron
Al8Mn5 particles of 0.09 to 0.4 lm in length occured in both SA and SB alloys; however, larger
Al8Mn5 particles of 4 to 10 lm in length were observed only in the SA alloy. The welding
process did not have a great effect on the populations of Al8Mn5 particles in these AZ31 welds.
The earlier columnar-equiaxed transition (CET) is believed to be related to the pre-existence of
the coarse Al8Mn5 intermetallic phases in the SA alloy as an inoculant of a-Mg heterogeneous
nucleation. This was revealed by the presence of Al8Mn5 particles at the origin of some equiaxed
dendrites. Finally, the columnar grains of the SB alloy, which did not contain coarse secondphase
particles, were efficiently restrained and equiaxed grains were found to be promoted by
adding 10 lm-long Mn particles into the fusion zone during resistance spot welding (RSW).