Effect of Al-rich α Phase on the Corrosion Properties of the Hot Chamber Die-Casting AZ91D Plate and Evaluation of the Corrosion Characteristic for Hydrogen Generation

• Main Authors: Kuo-Huang Wang, 王國皇
• Other Authors: Jun-Yen Uan
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/08229234382378517340

碩士 === 國立中興大學 === 材料工程學研究所 === 93 === The reason of the corrosion resistance decreasing of the die-cast AZ91D was the Al-rich α phase distributed in the die skin layer on the surface. In previous study, increasing the iron content caused the corrosion resistance decreasing of the Mg alloy. It was found that iron content (3.9wt%) in the Al-rich α phase distributed in the die skin layer on the die-cast AZ91D surface was greater than in the die-cast AZ91D’s average(0.005wt%) by the SEM-EDS analysis. To explore the corrosion relationship between the Fe content and Al-rich α phase, we melted two of the Al-rich α/ β composite phase alloys which had different Fe contents. After the polarization test on the Al-rich α/ β composite phase alloys, the current density (800~2000μA/cm2) with higher Fe content was greater than with lower Fe content (67~90μA/cm2). According the results, the reason of the corrosion resistance decreasing of the Al-rich α phase was its high iron content. The relationship between the corrosion rate and the hydrogen evolution rate of the Ni-rich AZ91D was shown as linear and positive. The Al-rich α/ β composite phase alloys and the Ni-rich AZ91D were used to generate the hydrogen with platinum wire catalyst in NaCl solution. As the experiment result, the hydrogen volume created from zero to ~ 500ml spent no more than 800sec in 5%NaCl solution in room temperature. The weight losses of the samples for hydrogen generation were in range of the 0.29g~0.62g. To prove the gas we generated was mostly hydrogen, the gas was ignited during the process. A slight burst is heard and the gas keeps burning afterward. This is due to the reaction between the hydrogen and the oxygen in the atmosphere. The by-product was analyzed by the Grazing Incident X-ray diffraction and proved as (Mg(OH)2) after comparing diffraction pattern. The present study might not only suggest a method to generate hydrogen but also promote the recycling of used magnesium products that were originally plated with Ni on their surface.