摩擦攪拌製程對ZK60鎂合金微結構與腐蝕性質影響之研究

Abstract

本研究對擠製態ZK60 (鎂鋅鋯)合金進行摩擦攪拌製程 (friction stir processing, FSP)，在加工過程中引發動態再結晶使晶粒細化，進而提高其抗腐蝕性。 原本的擠製態ZK60合金具有不均勻的晶粒尺寸及特定方位取向，經摩擦攪拌製程後，晶粒尺寸變得均勻且方位取向隨機。摩擦攪拌製程的加工參數包含旋轉工具的轉速及加工速度，本研究使用的三組加工參數分別為1800 rpm, 150 mm/min、1800 rpm, 200mm/min、1500rpm, 200 mm/min，得到攪拌區中心的平均晶粒大小分別為4.03 μm、3.66 μm、3.49 μm，這證實轉速越慢和越快的加工速度會產生越小的再結晶晶粒。 研究結果發現加工參數1500rpm, 200 mm/min的試片呈現最好的抗腐蝕性，腐蝕電流密度從擠製態ZK60合金的5.51×10^-5 A/cm²，降低到1.67×10^-5 A/cm²，極化電阻則從擠製態ZK60合金的315.2 Ω⋅cm2提高到 1009.8 Ω⋅cm2。觀察浸泡試驗後的腐蝕表面，發現擠製態ZK60合金由於晶粒尺寸不均勻導致不均勻腐蝕行為，其局部腐蝕的結果造成材料整體抗腐蝕性較差，摩擦攪拌製程ZK60合金則因晶粒尺寸均勻而呈現均勻腐蝕的狀態，有較好的抗腐蝕性。

In this study, extruded ZK60 (magnesium-zinc-zirconium) alloy was subjected to friction stir processing (FSP), which induced dynamic recrystallization during the process, leading to grain refinement and an improvement in corrosion resistance. The original extruded ZK60 alloy exhibited an uneven distribution of grain size and specific orientation. Following FSP, the grain size became uniform and the orientation was random. The processing parameters of friction stir processing (FSP) include the rotational speed of the rotating tool and the processing speed. This study employed three sets of processing parameters. The processing parameters included 1800 rpm, 150 mm/min; 1800 rpm, 200 mm/min; and 1500 rpm, 200 mm/min. These resulted in average grain sizes at the center of the stir zone of 4.03 μm, 3.66 μm, and 3.49 μm, respectively. These findings indicate that a slower rotational speed and a faster processing speed result in the formation of smaller recrystallized grains. The sample processed with parameters of 1500 rpm and 200 mm/min exhibited the most favorable corrosion resistance, with a notable decrease in corrosion current density from 5.51×10^-5 A/cm² for the extruded ZK60 alloy to 1.67×10^-5 A/cm², accompanied by an increase in polarization resistance from 315.2 Ω⋅cm² for the extruded ZK60 alloy to 1009.8 Ω⋅cm². The corrosion behavior of the extruded ZK60 alloy was observed to be uneven following immersion testing. This was attributed to the presence of an uneven grain size, which in turn resulted in a reduction in overall corrosion resistance. In contrast, the FSPed ZK60 alloy, with its uniform grain size, demonstrated uniform corrosion behavior and superior corrosion resistance.