Cover Picture: Materials and Corrosion. 11/2014

Abstract

Cover:The left image shows the corrosion potential distribution in volts on the cross‐sectional surface of a friction stir spot weld (FSSW) made in AZ31B magnesium alloy, obtained through the scanning reference technique (SRET). The color gradient represents the relative corrosion potential of the local area to the corrosion potential of the base metal. The weld nugget is observed to be noble to the host material, resulting in the formation of a macrogalvanic cell and subsequent accelerated corrosion in the boundary between the weld nugget and the base metal. An optimized microcapillary polarization methodology was utilized to analyze the corrosion rates of individual microstructural zones. The pictures on the right show the capillary used for local polarization experiments, and the corroded spot on the sample that was produced as a result of testing.Microcapillary polarization confirmed the noble behaviour of the stir zone, and demonstrated lower corrosion rates of this microstructural zone in 0.1 M NaClO4 as compared with the rest of the weld. Contrary to the SRET results, microcapillary polarization investigation revealed that there is no potential gradient between the thermo‐mechanically affected zone and the base metal.More detailed information can be found in: Y. Savguira, T. H. North, S. J. Thorpe, Microcapillary polarization measurements of friction stir spot welds made in AZ31B magnesium alloy, Materials and Corrosion 2014, 65, 1055.