冷軋延對ZK60擠製材的拉伸與疲勞性質之影響

The effects of cold-rolling on the tensile and fatigue properties of as-extrusion ZK60 alloy

王士銘(Shih-ming Wang)

指導教授 ： 李雄

國立中央大學/工學院/機械工程研究所碩士在職專班/碩士(2012年)

摘要

ZK60鎂合金是目前所有商用鎂合金中強度最高的一種，其熱擠製型材的降伏強度達到300MPa，已經超過T6狀態下的7010A鋁合金，與12Mn合金鋼相當。
　　本研究之目的為探討ZK60鎂合金經8%冷軋後之微結構、拉伸與疲勞性質。經顯微組織觀察與XRD分析，兩種材料主要相為α-Mg，並伴隨少量MgZn2相。此外，ZK60之晶粒尺寸變化大，判斷其原因為在擠製過程中，材料於不同部位的塑性變形量有所不同，造成再結晶的程度亦不同所致。
　　機械性質方面，ZK60擠製原材的降伏強度為229MPa，而擠製ZK60+8% 冷軋，強度提昇至269MPa，顯示冷軋後大量冷加工應變能使強度明顯提昇，提昇率為17.4%。抗拉強度由254MPa，提升到冷軋後的273.5MPa，提升率為7.6%；而材料的延伸率由擠製材48%減少到經8%冷軋延21%。兩者的結果顯示冷軋後，大量的加工應變能使材料的強度提升但延性下降，顯示出典型的加工硬化結果。
　　在疲勞測試方面，ZK60擠製原材與擠製ZK60+8% 冷軋兩種材料的疲勞限分別為71MPa和81MPa，疲勞強度提升了14%。

關鍵字

抗拉強度 ； 疲勞強度 ； ZK60鎂合金 ； 冷軋延

並列摘要

This research focuses on the tensile and fatigue properties of normal and cold-rolled extrusion ZK60 alloy. ZK60 magnesium alloy is a commercial magnesium alloy which is one of highest intensity. Its yield strength of type of hot extrusion reaches 300MPa. Over 7010A aluminum alloy and close with the 12Mn alloy steel. Thus its strength is almost all the material on its advantage in the highest, so ZK60 magnesium alloy used in the transport apparatus.

About microstructure, The two materials are rendering conventional extrusion ZK60 organizational structure, the main crystalline phase is α-Mg but the β phase is not visible because it is too small. However, its grain size varied that causes in the different levels of plastic deformation in different parts of materials, resulting in the levels of recrystallization is also different.

About mechanical properties, the yield strength of ZK60 extrusion original material is 229MPa, the extrusion ZK60 +8% cold-rolled increased to 269MPa, The results show a large number of cold work strain energy can significantly enhance the strength about increase rate of 17.4% after cold-rolled. The tensile strength creased by 7.6% after cold rolling, as 254MPa to 273.5MPa, the average elongation rate decreased from 48% to 21%, results show caused by the cold work strain energy increase.

The fatigue limit of ZK60 extrusion original material and the extrusion of ZK60 +8% cold-rolled is 71MPa (approximately 28% of UTS) and 81MPa (approximately 29.6% of the UTS), a 14% increase in fatigue strength.

並列關鍵字

Tensile strength ； Ultimate strain ； Fatigue limit ； Cold-rolled ； ZK60 magnesium alloys

參考文獻

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