Hisakimi Notoya

Improvement in Corrosion Fatigue Resistance of Mg Alloy Due to Plating

Magnesium alloys are very attractive as structural materials, because they are extremely light, possessing excellent specific tensile strength, good stiffness, good cutting performance, and good vibrational absorption [1]. In addition, the recycling energy requirement of these alloys is only 4–5% of the energy required to obtain magnesium from the ore [1]. Due to their energy and weight saving characteristics, magnesium alloy are considered to be good candidates for material in auto parts, portable personal computers, and telephones. However, magnesium alloys have not been extensively used until recently, because of their vulnerability to corrosion. When considering the use of magnesium alloys as structural materials, a thorough understanding of the corrosion-fatigue characteristics is necessary to reflect the results in machine design. Further, improvement in the corrosion fatigue performance of magnesium alloys is highly desirable to realize their potential as structural materials. Surface treatments, such as coating or plating of the material surface have been examined for enhancement of the corrosion fatigue resistance of magnesium alloys, and in general they have not been successful. In this paper, two types of plating treatments, i.e., electroless-Ni-plating [2] and electrolytic Ni-plating [3] were applied to the Mg alloy AZ31 to improve the corrosion fatigue resistance of the alloy. Corrosion fatigue lives and fatigue behavior of the specimens were investigated in detail and their mechanisms will be also discussed. Specific contents in this chapter are summarized as follows. In section 2 [2], fatigue tests were performed on electroless nickel-plated magnesium alloy specimens in laboratory air and 3% sodium chloride solution. In laboratory air, the effect of surface treatments (plating, blasting and polishing) on the fatigue lives of specimens was found to be minimal. However, in 3% sodium chloride solution, the electroless Ni-plated specimens were found to have shorter fatigue lives than those of the polished and blasted specimens. In order to study the fatigue mechanisms, successive observations of the specimen surfaces were conducted during the fatigue process in both laboratory air and sodium chloride solution. Observations of the fracture surfaces were also conducted to clarify the fatigue mechanism. In section 3 [3], the fatigue behavior of electrolytically nickel-plated Mg alloy both in laboratory air and in a corrosive environment (3% NaCl) were described. The fatigue

Electrochemical Dissolution Characteristics of Magnesium Alloy Produced by Roll Compaction Process

The extruded AZ31B Mg alloy specimens using powders fabricated by roll compaction processing (RCP) was prepared, and their corrosion behavior has been investigated through the polarization test, electrochemical impedance spectroscopy test, immersion test and SEM observation in comparison to that of the conventional AZ31B Mg alloy, hereafter shortened as I/M specimen. The extruded AZ31B Mg alloys using RCP powder showed little change in Ecorr irrespective of number of pass cycles. Both anodic and cathodic current density suppression of the RCP specimens became larger with an increase in number of pass cycles. It was also confirmed that the corrosion characteristics of the RCP specimens depended strongly on their structural morphology and that the corrosion resistance of the RCP specimens subjected to 50 pass cycles was nearly same as that of the I/M specimen.

Residual stress in dry-ground Al-Si alloy castings.

Al-Si alloy castings, AC3A, were dry ground at different depth of cut, work speed and wheel speed. Both the residual stress and residual shearing stress in the specimens were measured. Normal residual stress generated in the grinding direction was tension at the surface of the specimens. Tensile residual stress at the surface was small. The residual shearing stress at the surface decreased with the increase in the depth of cut and work speed. Textures at the grinding surface and slightly inner regions of the specimens were investigated. Textures at the grinding surface were similar to each other for all grinding conditions, while textures at the slightly inner region were different from those at the surface. The influence of the alloy structure on the residual stress was discussed.