"Mg-xLi (x=11, 14wt.%)鎂鋰合金機械性質之研究"

Abstract

本研究針對極輕質LZ141鎂鋰合金，進行不同之固溶處理與冷軋延等熱機處理來改變其顯微結構，並藉由顯微組織觀察、XRD分析、硬度、衝擊及拉伸試驗等，來了解不同的熱機處理對LZ141合金機械性質之影響。研究結果顯示，LZ141合金之硬度與強度具有相同的變化趨勢，熱軋延之LZ141經冷軋延後硬度及抗拉強度皆上升，但經固溶處理後，抗拉強度及硬度皆下降，顯示固溶處理對於LZ141無強化效果。對SS+CR80%之試片於垂直於軋延方向之(90o)拉伸時，抗拉強度可達176.4MPa(比抗拉強度為126.9)。HR LZ141於不同方位進行衝擊試驗，發現凹槽垂直於軋延方向之方位的衝擊值最高，為0.51J/mm2，且在不同的溫度下進行衝擊試驗，發現其衝擊值對溫度的變化並不敏感，即使到-196oC其值仍在0.4 J/mm2左右。LZ141有明顯的Portevin–Le Chatelier(PLC)現象，利用拉伸實驗結果計算與PLC相關之參數。本研究同時探討 LAZ1110+Be+Sc(LAZ1110BS)合金經固溶處理與冷軋延等熱機處理後之機械性質，並與LAZ1110合金做比較。研究結果顯示，LAZ1110BS之最佳強化效果為在空氣爐中進行固溶處理且快速水淬，再進行冷軋延80%，其抗拉強度高達280MPa(比抗拉強度為189.2)。而LAZ1110BS經固溶處理後冷軋延，也可大幅減緩其經固溶處理強化後於室溫下之機械性質劣化的現象。LAZ1110合金藉由RSP製程製作成箔帶(LAZ1110R)，其硬度可以高達111.3Hv，比塊材的58.1Hv要高上許多，可能與薄帶內α相的析出有關。

Various thermomechanial treatments are conducted to strengthen the extremely light LZ141 and LAZ1110 magnesium alloys. The strengthened alloys are investigated by microstructural observation, XRD analysis, microvickers hardness, impact and tensile tests. Experimental results indicate both hardness and tensile strength of hot-rolled (HR) alloys increase after cold rolling (CR), but decrease after solid-solution treatment (SS). The SS process has no strengthening effect. For SS + CR80% specimens, the maxium tensile strength is 176.4MPa which is tensiled in the direction perpendicular to the rolling direction. The impact test of HR 141 alloy shows the highest impact value is 0.51J/mm2 which occurs at the notch direction perpendicular to the rolling direction. The impact value is 0.4 J/mm2 at -196oC and is not sensitive with the testing temperature. The tensile curves of HR LZ141 alloy have obviously Portevin-Le Chatelier (PLC) effect. The strengthening mechanism of LAZ1110 alloy with little Be and Sc (LAZ1110BS) is also investigated and compared to that of LAZ1110 alloy which had studied in this group two years ago. The best method to strengthen LAZ1110BS is solid-soluted in air furnace, water quenched and then cold-rolled 80%, which can reach the tensile strength of 280MPa, i.e., specific tensile strength of 189.2. As the same time, LAZ1110BS thermomechanical-treated by SS+CR80% can retard the degradation of the hardness when specimens are aged at room temperature for long time. The hardness of LAZ1110 ribbons prepared by rapid solidification process has the handness of 111.3Hv, which is much higher than bulk LAZ1110 alloy which has the harndess of 58.1Hv.