Browsing by Author "Wang, Che-Chung"

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A study of weldability and fracture modes in electron beam weldments of AZ series magnesium alloys
(2006-11-05)
Chi, Chao-Ting
;
Chao, Chuen-Guang
;
Liu, Tzeng-Feng
;
Wang, Che-Chung
;
材料科學與工程學系
Given the growing need for environmental protection and lightweight construction, electron beam welding (EBW) is becoming the most important welding technology because it can compensate for the poor formability of magnesium alloys. This paper examines interactions between the properties of three AZ series magnesium alloys and welding conditions. The EBW process can yield four kinds of defect in a weld: cavities, the heat-affected zone (HAZ), undercuts, and root concavities. These defects obviously induce stress concentrations in the weld, and may seriously damage its strength. Additionally, the distribution of precipitates (gamma phase, Mg17Al12) in the fusion zone (FZ) changes from a relatively small number of scattered particles to a dense population of dendrites as the Al content of the magnesium alloy increases. Under excessive tensile stress, alloy weldments break in one of two fracture modes: an irregular FZ fracture, or a regular HAZ fracture. AZ31B usually exhibits the former mode and AZ91D the latter, while AZ61A exhibits each mode half the time. The overall weldability, which depends on the random distribution of these precipitates and defects, is found to be greatest for the AZ61A alloy. The best process window, on the other hand, is found for the AZ91D alloy. Finally, we obtain optimum parameters for the EBW process and empirical formulae for the weldment strength as a function of these parameters. These results are closely related to each other. (c) 2006 Elsevier B.V. All rights reserved.
Relational analysis between parameters and defects for electron beam welding of AZ-series magnesium alloys
(2008-06-19)
Chi, Chao-Ting
;
Chao, Chuen-Guang
;
Liu, Tzeng-Feng
;
Wang, Che-Chung
;
材料科學與工程學系
In the last half century, lightweight magnesium alloy has gradually shifted from military applications to civil applications. More noteworthy is that its low melting point, high thermal conductivity, and superior fluidity are good for weld pool flow and welding parameter research. This paper presents a novel approach to these characteristics, which analyzes the influences of electron beam welding parameters on weldment strength and defect formation by linking Taguchi's method with the grey relational analysis. Not only are the parameter contribution and the defect weight individually quantified, but also the relationship between welding parameters and defect dimensions can also be obtained this way. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.