AZ型鎂合金微銲接之最適參數研究

Abstract

本論文係利用Nd: YAG雷射對AZ系列鎂合金進行銲接，並應用田口方法來找出雷射銲接最適參數，並利用變異數分析法找出雷射銲接參數對品質特性之影響。以田口方法獲得最適參數後，以此參數再銲接AZ31與AZ31-61異質銲接。銲後所得之銲道以實體顯微鏡觀察外觀並量測其深寬比，再對各試片進行拉伸測試、硬度測試以評估其機械性質。結果獲得到下列幾點結論：

1.利用田口方法所得到的雷射銲接最適參數，經過測試後所得到之品質特性擁有再現性。

2.經過雷射銲接後所有銲道硬度值比母材高，且發現到鋁含量高的AZ61其銲道硬度值比AZ31高。此現象係因銲道的結晶型態與合金成份有關。

3.在AZ61、AZ31與AZ31-61異質銲接都有發現凝固熱裂，以AZ31熱裂情況最嚴重。因鎂合金銲接後因凝固熱裂縫之影響，導致抗拉強度降低。

4.EDS分析後，可發現在熱裂縫表面的鋅含量比銲道金屬高，應該是造成熱裂縫的原因。且發現鋁含量增加可降低鎂合金熱裂敏感性。

The purpose of this study was to determine the optimal parameters of mircowelding of magnesium alloys AZ31and AZ61. Nd: YAG laser machine was used to do welding process and Taguchi Method was used to do optimization. Furthermore, ANOVA (analysis of variance) was utilized to find the quality characteristics of importance in the laser welding parameter. The microstructure of the fusion zone was observed by OM and the aspect in the fusion zone was measured. Tensile test and microhardness test were conducted to evaluate the mechanical properties of Mg-alloys. The following results were found from this study. 1. Very good reproducibility of this experimentation can be obtained by using the optimal parameters of mircowelding from Taguchi Method.

2. After laser welding, the hardness of fusion zone is higher than that of base metal. The fusion zone’s hardness of AZ61 is higher than that of AZ31.

3. Solidification cracking can be observed in all specimens after laser welding, especially in AZ31. These solidification cracking will reduce the tensile strength in the fusion zone.

4. From EDS results, the Zn content in the cracking surface is higher than weld metal, and this maybe is the reason for making the solidification cracking. It is also found that the increases of Al content can decrease the hot cracking sensitivity.