AZ31B鎂合金銲接角變形與殘留應力之分析

Analysis of welding on angular distortion and residual stresses in AZ31B magnesium alloy

石晶瑩(Ching-Ying Shih)

指導教授 ： 鄭慶民 ； 周長彬

國立臺灣師範大學/科技學院/工業教育學系/碩士(2006年)

摘要

本論文主旨在探討AZ31B鎂合金銲接角變形與殘留應力之變化情形。為模擬分析銲接過程中溫度、應力與角變形之變化情形，本研究採用熱彈塑性理論，且應用熱-結構耦合元素及考慮非線性材料特性等來進行銲接之有限元素分析。在模擬分析過程中，主要區分為熱學模式與力學模式分析理論。在實驗上，實驗材料選用AZ31B鎂合金，銲接方法則採用惰氣鎢極電弧銲，並以熱電偶記錄銲接時的熱循環溫度，而冷卻至室溫後，量測其角變形量。
本研究結果顯示，在施加拘束條件下的銲接過程中，由於銲接熱源的高溫作用，將導致銲道附近有較高的溫度梯度存在，因而接近銲接熱源的區域則受到高溫而膨脹，但又受到遠離銲接區域的束縛，因此在銲接熱源附近會產生壓縮熱應力。隨著銲接熱源的消失，在靠近銲道附近的區域因受到冷卻而收縮，但又受到遠離銲道區域的束縛，因此在銲道附近將會產生拉伸殘留應力。在拘束條件不同之情形下，分析結果發現平板末端為不拘束者，其殘留應力將比拘束者為小。在不同銲接速度之情形下，分析結果發現銲接速度快者，其殘留應力比速度慢者為小。在無拘束條件下，分析結果與實驗結果比較發現銲件兩端將呈現向上翹起之現象。

關鍵字

鎂合金 ； 角變形 ； 殘留應力 ； 有限元素

並列摘要

This study was to investigate the fundamental characteristics of the temperature and stress fields in bead-on-plat during welding process. The thermo-elastic-plastic theory and the thermo-mechanical coupled elements were employed in this analytical model with temperature dependent material properties. A two-dimensional model using ANSYS finite element method was designed to estimate the magnitude and distribution of the temperatures, thermal stresses, and residual stresses in weldment. The theoretical considerations can be divided into the thermal and mechanical model. AZ31B magnesium alloy were used as test specimens, which were welded with an GTAW. The thermal cycle temperature while welding with the thermocouple record, and cool to the room temperature, quantity examines its angular distortion amount.
The analytical results were compared with the experimental data containing temperatures and angular distortion. Because of the heat source is concentrated locally, the temperature fields adjacent to the heat source are rather steep. The transient thermal stresses are in compressive state since the expansions of these regions are restrained by surrounding cold metal that is at lower temperatures. As the heat source had passed by, the fusion zones have been cooled and hence have a tendency of contraction. A great tensile residual stress was produced in solidified welds, and then rapidly decreased to zero over a distance several times the welded zone. In a situation that restrained conditions are different, the residual stress of non-restrained condition is small than the restrained one. In a situation that weld the speed differently, the speed of the residual stress of welding quickly is small than the slow one. There is a fairly good agreement between theoretical analysis and experimental results using the finite element method.

並列關鍵字

Magnesium alloy ； angular distortion ； residual stresses ； finite element