G. Ben-Hamu

Galvanic Weld Metal-Base Metal Corrosion in AZ31 Magnesium Weldments

Arc welds were made on wrought AZ31 magnesium plate using a variable polarity gas-tungsten arc process with AZ61 filler wire. The aluminum content of the weld metal was systematically varied using inserts pre-placed in the weld joint, machined from magnesium die-cast alloys AM20, AM50, AM60, and AZ91. When immersed in 3.5% NaCl + Mg(OH)2 solution at room temperature, pitting corrosion was found to initiate in the weld heat affected zone, spread briefly to the weld metal, and then concentrate in the base metal. Galvanic couples were examined between wrought AZ31 and die-cast alloys to further examine galvanic behavior between wrought and cast materials. Results showed that the cast material was anodic relative to the wrought material over long periods of time, unlike what was observed for weldments. Details of this study will be presented and results will be related to alloy aluminum content and the ability to passivate.

The influence of Ag and Si additions on the electrochemical behavior in extruded Mg‐Zn alloys

Development of new wrought magnesium alloys for the automotive industry has increased in recent years, due to their high potential as structural materials for low density and high strength/weight ratio demands. However, the poor mechanical properties and low corrosion resistance of the magnesium alloys have led to a search for new kinds of magnesium alloys, for better strength, ductility, and high corrosion resistance. The main objective of this research is to investigate the corrosion behavior of new magnesium alloys: Mg-Zn-Ag (ZQ) and Mg-Zn-Si (ZS). The ZQ6X and ZS6X alloys were prepared using the hot extrusion method. AC and DC polarization tests were carried out on the extruded rods, which contain different amounts of silver or silicon. The microstructure was examined using optical and electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results showed that the silver addition decreased corrosion resistance. The addition of silicon also affected corrosion behavior. These results can be explained by the effects of alloying elements on the microstructure of Mg-Zn alloys, such as grain size and precipitates caused by the change in precipitation, and by recrystallization behavior.

Studies on the Influence of Chloride Ion Concentration on the Corrosion Behavior of ZSMX Magnesium Alloy

The paper presented reveals the influence of chloride ion concentration on the corrosion and electrochemical behavior of new ZSMX wrought magnesium alloy in NaCl solution. The experimental techniques used include potentiodynamic polarization tests. The corrosion rate usually increased with the increase in chloride ion concentration. This result can be explained by the distribution of intermetalics.

The Relation between Microstructure and Corrosion Behavior of New Mg-Al-X Alloys for Transportation Application

New die cast magnesium alloys have increasingly been developed in recent years for the automotive industry due to their high potential as structural materials for low density and high strength/weight ratio demands. However, their poor mechanical properties and low corrosion resistance have led to a search for new kinds of magnesium alloys with better strength, ductility, high temperature behaviour and high corrosion resistance. The main objective of this research is to investigate the corrosion behaviour of new die cast magnesium alloys: Mg-Al-Ca, Mg-Al-Sr. AC and DC polarization tests were carried out on the new alloys. Microstructure was examined using optical and electron microscopy (SEM) and EDS. The additions of Sr and Ca affected the corrosion behaviour. These results can be explained by the effects of alloying elements on the microstructure of Mg alloys such as grain size and precipitates caused by the change in precipitation.

Microstructure of Ti-45Al-5Nb after Cathodic Charging

Gamma titanium aluminide material, cast Ti–45Al–5Nb (at.%), was electrochemically precharged with hydrogen in the cathodic charging mode at a current density of 50 mA/cm2 for times ranging from 6 to 48 h. XRD and microstructure investigations by means of electronic microscopy were used for analyzed the influence of hydrogen on the microstructure.