Magnesium Technology 2017: Corrosion
Sponsored by: TMS Light Metals Division, TMS: Magnesium Committee
Program Organizers: Kiran Solanki, Arizona State University; Dmytro Orlov, Lund University; Alok Singh, National Institute for Materials Science; Neale Neelameggham, Ind LLC

Thursday 8:30 AM
March 2, 2017
Room: 5B
Location: San Diego Convention Ctr

Session Chair: Kiran Solanki, Arizona State University; Ilaksh Adlakha, Arizona State University

8:30 AM  
Role of Mechanical Loads on the Corrosion Behavior of Mild-Steel and AE-44 Structural Joint: Ilaksh Adlakha1; Benyamin Gholami1; Nitin Muthegowda2; Kiran Solanki1; 1Arizona State University; 2COMSOL
    Here, we present an experimentally validated numerical model for an AE44 (Magnesium alloy) and mild steel galvanic couple subjected to a mechano-electrochemical process. In order to examine the effect of mechanical loads on the corrosion behavior, the galvanic couple was subjected to static and fatigue loads. Results show that, a remarkable increase was observed in the pit depth near galvanic interface, due to the presence of plastic strain within the anodic electrode. In the case of both mechanical loading scenarios, an increase in localized corrosion around the galvanic junction was observed, however, it was far more severe in the case of fatigue loading. Furthermore, the effect of electrolyte depth and electrode surface area ratio on the galvanic corrosion behavior was studied. The decrease of electrolyte depth was found to promote the localized corrosion behavior. In the case of smaller cathodic surface areas, the localized corrosion process was intensified.

8:50 AM  
Corrosion and Creep Resistance of ThixomoldedŽ Magnesium Alloys: Ricardo Buzolin1; Hajo Dieringa1; Carsten Blawert1; Hagen Frank1; Chamini Mendis1; Andreas Lohmüller2; Karl Kainer1; Norbert Hort1; 1Helmholtz-Zentrum Geesthacht; 2Neue Materialien Fürth Gmbh (NMF)
    Process optimization is one pathway to maximizing strength of a given alloy. Thixomolding is a semi-solid casting process that combines pores reduction with a typical bimodal grain size distribution that can lead to enhanced strength. AZ91D and MRI153 were processed via thixomolding using two different processing conditions to change fraction solid particles at the point of injection into the mold. The tensile properties, creep resistance and corrosion behavior of the alloys were investigated. The creep resistance was measured in the range of 135-150 oC and stresses of 50-85 MPa. The corrosion behaviour was measured via hydrogen evolution for the two alloys and was smaller than that for pure Mg. The MRI153 alloy showed improved creep resistance compared with the AZ91D. The differences in the property profile of the chosen alloys are correlated with their chemical compositions as well as with different microstructures obtained through the different processing conditions.

9:10 AM  
Corrosion Properties of Mg-6Al-0.3Mn-aSn-bZn Alloys: Chang Dong Yim1; Sang Kyu Woo2; Nam Ryong Kim2; Ha Sik Kim1; Bong Sun You1; 1Korea Institute of Materials Science; 2University of Science and Technology
    The effect of addition of Sn and/or Zn on corrosion properties of Mg-6Al-0.3Mn alloy was investigated systematically by immersion and salt spray tests. In case of immersion test, average corrosion rate increased by addition of 1 wt.% Sn but it decreased by addition of 1 wt.% Zn. When the half of the amount of Sn addition was replaced by Zn, the average corrosion rate decreased in comparison with the average corrosion rate of Mg-6Al-0.3Mn-1Sn alloy. In case of salt spray test, the change of average corrosion rate according to composition of the alloy was similar to the result of immersion test. It seemed that the change of corrosion properties according to composition of the alloy was strongly related to the microstructural changes including the sort, fraction and morphology of second phase.

9:30 AM  
Corrosion of Magnesium-aluminum (Mg-Al) Alloys – An Interplay between Al Content and CO2: Mohsen Esmaily1; Jan-Erik Svensson1; Lars-Gunnar Johansson1; 1Chalmers University of Technology
    Considering the practical applications of Mg alloys, which are mainly in automobiles and housing utensils, Mg alloys are frequently used in atmospheric conditions. In this research, we systematically exposed several Mg alloys (including AM20, AM50, and AZ91) to different atmospheric environments with different concentrations of environmental variable. A detailed investigation was performed to understand the role of NaCl, CO2, SO2 and temperature using carefully controlled laboratory experiments. The study elucidates the interplay between the alloys’ microstructural constituents (α, β, η and casting pores) and the changes in the atmosphere, and, thus, provides a mechanistic understanding of the atmospheric corrosion behavior of Mg alloys. It is expected that the findings presented of this study can contribute interpreting the corrosion behavior of Mg alloys in different climates.

9:50 AM  
Excimer Laser Processing of Al Containing Mg Alloys for Improved Corrosion Resistance: Michael Melia1; John Scully1; James Fitz-Gerald1; 1University of Virginia
    The implementation of Mg-based alloy components in Cl- containing environments is limited by the poor intrinsic corrosion resistance of the starting alloys. Galvanic coupling of secondary phase particles to the Mg matrix combined with Mg’s low electrochemical potential result in accelerated cathodic kinetics, the controlling reaction of Mg corrosion. To mitigate this behavior, localized dissolution of secondary phases by laser processing was performed on three Al containing Mg alloys; AZ31B-H24, AM60B, and AZ91D. Complete and mixed dissolution of secondary phases was observed by electron and chemical microscopy. An order of magnitude increase in the electrochemical impedance estimated corrosion resistance and order of magnitude reduction in cathodic kinetics was observed for the laser processed specimens immersed in a 0.6M NaCl solution (18 to 60 hours). The dramatic increase in corrosion resistance stems from the reduced density of electrochemically noble secondary phase particles and localized enrichment of Al.

10:10 AM Break

10:30 AM  
Effect of Al and Sn on Discharge Behavior of Mg Alloy as Anode for Mg-Air Battery: Kim Sang-hyun1; Park Jun-ho1; Kim Hee-san2; Kim Jae-joong1; Kwon Oh-duck1; 1POSCO; 2Hongik university
    Recently, Mg-air battery has been researched as an attractive power source due to its high specific discharge capacity, safety, and eco-friendly properties. In this study, we researched the effect of Al and Sn on discharge behavior of Mg alloy as anode for Mg-Air battery. The test sample was prepared by gravity cast and rolled process. The Mg-Al-Sn alloys were rolled to the 2mm thickness at rolling temperature of 573K and rolling reduction of 10~20%. Microstructures of the test samples were observed by optical microscopy and scanning electron microscopy. Discharge behavior was investigated by constant current discharge test. With increase of Al and Sn contents, hydrogen evolution rate of test samples decrease. And, with increase of Sn contents, discharge properties of test samples increase especially at high current (60mA)

10:50 AM  
Utilization of a Partially Non-aqueous Electrolyte for the Spatial Mapping of Mg Corrosion Using a Model Mg-Al Electrode: Leslie Bland1; Rebecca Schaller2; John Scully1; 1University of Virginia; 2Sandia National Laboratory
    In-situ techniques to spatially map micro-galvanic corrosion are particularly important for alloys with heterogeneous microstructures. In particular, scanning electrochemical microscopy (SECM) has been utilized to map microstructural features on Mg which may control the corrosion rate. However, rapid corrosion rates of Mg in fully aqueous environments interfere with mapping capabilities. A mixed aqueous and non-aqueous electrolyte, containing methanol and H2O, is proposed which is capable of mapping the active corrosion on Mg with time. However, thorough understanding the effect of methanol additions on the corrosion rate was required. Therefore, the intrinsic corrosion rates of Mg in varying amounts of methanol (0 wt% to 100 wt%) were investigated using electrochemical impedance spectroscopy (EIS) by exploring the corrosion rate on an Al wire embedded in Mg as a galvanic couple. The nature of the non-aqueous electrolyte on the EIS response is discussed.

11:10 AM  
Voltammetric Studies of Extruded Pure Magnesium in Different Electrolytes and Its Corrosion Morphology: Petra Maier1; Leon Gentzsch1; Norbert Hort2; 1University of Applied Sciences Stralsund; 2Helmholtz-Zentrum Geesthacht
    This study concerns the voltammetric behavior in different electrolytes of pure Magnesium processed by direct extrusion. The recrystallized microstructure is fine grained and homogeneously distributed. Magnesium is known to suffer pitting corrosion when exposed to chloride solutions. To cause a high anodic dissolution, corrosion has been evaluated with potentiodynamic polarization in Ringer Acetate, HBSS and DMEM up to 500mV. The anodic current density within the active corrosion region and the current density and potential for passivation were used to compare the corrosion behavior. Corrosion in DMEM showed a tendency to passivation, Magnesium in HBSS only pseudo-passivated. Corrosion in Ringer-Acetate showed the highest current density without passivation up to 500mV. Corrosion morphology is discussed by using the pitting factor and size of corroded area. These values are correlated to the current density-potential curves. With decreased corroded area due to passivation the pitting factor increases. Corrosion behavior is compared to immersion tests.