Applicability of CO2 Laser on AZ61and AZ80 Extruded Magnesium Alloys Welding Research

• Main Authors: Tsung-yu Yang, 楊宗育
• Other Authors: Hsien-Lung Tsai
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/49937519636368158526

碩士 === 國立臺灣科技大學 === 機械工程系 === 96 === Investigation of CO2 laser welding has been done to AZ61 and AZ80 magnesium alloy extrusion sheet. Material without heat treatment has been compared with material which heat treated prior to welding. The aim of this research was to study the effect of different heat input of CO2 laser welding on mechanical properties, microstructure, chemical composition and welding defects of the magnesium alloy extrusion sheet in order to improve the weldability. Base metal and weld metal were observed with the scanning electron microscope. Energy dispersive X-ray spectroscopy analysis reveals that the heat treatment materials have more Al and Zn element segregation in grain boundary. When the alloy with higher aluminum content has wider weld zone in the same heat input relatively. Near the fusion line becomes more Al element segregation and in the weld region the dendritic compounds relatively contain high Al. Experimental results showed that the width of weld cross section was increased with the increment of heat input, and the fusion line has permeated into base metal. The low heat input would increase tensile strength, because the fusion zone has finer crystal microstructure and the heat affected zone width was reduced. It is difficult to produced unstable plasma which leads to weld porosity. But high welding speed brought the big supercooling area ,fusion line solidify in advance prior to partially melted zone (PMZ), cause liquation cracking in the PMZ which lead to loss of tensile strength. Segregation phenomenon of some Al element in liquation cracking has been taken to analyze by EDS.