應用田口法於AZ31鎂合金薄板摩擦攪拌銲接之最佳參數設計

Optimization of Friction Stir Welding on AZ31 Thin Plate Using Taguchi Method

鄭凱維(Cheng Kai-Wei)

指導教授 ： 劉傳璽 ； 尤尚邦

國立臺灣師範大學/科技與工程學院/機電工程學系/碩士(2022年)

https://doi.org/10.6345/NTNU202200287

摘要

本研究使用精密型五軸加工機，配合自行設計得夾具夾持厚度為1 mm之AZ31鎂合金薄板試片，固定於工作平台上進行摩擦攪拌銲接，使用田口法減少實驗次數並找出最適參數組合以得到最佳的抗拉強度，用L9的田口直交表設計加工參數，三種因子與各三種水準分別為攪拌頭肩部尺寸(2、2.5、3 mm)、主軸轉速(14000、15000、16000 rpm)以及進給速度(5、10、15 mm/min)。銲接後再進行銲道的表面觀察、微硬度試驗、金相顯微組織觀察、拉伸試驗及掃描式電子顯微鏡觀測分析，實驗後得到以下幾項結論：
1. 銲道的孔洞缺陷直接影響銲道的抗拉強度，從拉伸試驗的斷裂面能看出其斷裂位置並非原本的對接邊，而是銲道造成的孔洞處斷裂，抗拉強度最高的編號5試片其孔洞缺陷最小，抗拉強度最高，能判斷孔洞缺陷對銲道抗拉強度有非常大的負面影響。
2. 最高的抗拉強度為編號五試片，其參數為2.5 mm肩部尺寸、15000 rpm、15 mm/min，抗拉強度為169.052 Mpa，約為母材強度的65%，最低的抗拉強度為編號1試片，其參數為2 mm肩部尺寸、14000 rpm及5 mm/min，抗拉強度為30.804 Mpa，為母材強度的11%。
3. 編號5號試片出現延性破壞的酒窩狀(dimple)組織，顯示本試片在拉伸過程中產生了塑性變形，其他八組試片發現材料的斷面呈現劈裂面或自由表面，尚未完全塑性變形便破斷，可以得知其他組別試片的破斷面皆為脆性破壞。
4. 透過田口法，找出之最適參數為A2(2.5 mm肩部尺寸)、B2(15000 rpm)、C3(15 mm/min)參數組合，其剛好為實驗參數配置的編號五號試片。

關鍵字

鎂合金 ； 摩擦攪拌銲接 ； 田口法 ； 抗拉強度

並列摘要

In this study, a small five-axis machining machine was used with self-designed fixtures to hold AZ31 magnesium alloy sheet specimens with a thickness of 1 mm, fixed on the working platform for friction stir welding. The Taguchi method was used to reduce the number of experiments and find the optimal parameters. Combined to obtain the best tensile strength, the processing parameters are designed with the Taguchi direct table of L9. The three factors and the three levels are respectively the shoulder size of the stirring head (2, 2.5, 3 mm) and the spindle speed (14000, 15000, 16000 rpm) And the feed speed (5, 10, 15 mm/min). After welding, surface observation, microhardness test, metallographic microscopic test, tensile test and scanning electron microscope observation and analysis. After the experiment, the following conclusions were obtained:
1. The highest tensile strength is the No.5 test piece, whose parameters are2.5 mm shoulder width, 15000 rpm, 15 mm/min, and the tensile strength is 169.052Mpa, which is about 65% of the strength of the base metal, and the lowest tensile strength is No. 1 test piece, its parameters are 2 mm shoulder width, 14000 rpm and 5 mm/min, and the tensile strength is 30.804 Mpa, which is 11% of the base metal strength.
2. The hole defect of the weld bead directly affects the tensile strength of the weld bead. From the fracture surface of the tensile test, it can be seens that the fracture position is not the original butt edge, but the hole caused by the weld bead. The test piece No.5 has the smallest hole defect and the highest tensile strength. It can be judged that the hole defect has a very negative impact on the tensile strength of the weld bead.
3. The test piece No.5 has a dimple structure with ductile failure, which shows that this test piece has plastic deformation during the stretching process. It is broken before complete plastic deformation. It can be seens that the fracture surfaces of other groups of test pieces are all brittle failures.
4. Through the Taguchi method, the optimal parameters were found to be the combination of A2 (2.5 mm shoulder diameter), B2 (15000 rpm), and C3 (15 mm/min), which is exactly the No. 5 test piece configured by the experimental parameters.

並列關鍵字

magnesium alloy ； friction stir welding ； Taguchi method ； tensile strength

參考文獻

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