鎂合金具有低密度、制振性佳及高比強度等優點，因此常用於交通工具與3C產業等之結構材料。在鎂合金中添加鋰元素可改善鎂合金之成型性，且有降低密度的效果。前人研究指出，雙相鎂鋰合金擠型材的第二相α相以板狀分散在基地中，於受力情況下易成為破壞起始點。為達改變第二相分布型態之目的，本研究以摩擦攪拌製程(FSP)對Mg-9Li-2Al-1Zn (LAZ921)雙相鎂鋰合金擠型板材進行改質，並以安定化熱處理使材料穩定。之後將擠型材、摩擦攪拌材(FSP材)以及摩擦攪拌並進行安定化熱處理的材料(FSP-S材)進行拉伸試驗，以觀察改質前後破壞型態的改變。另外將三種材料以沖剪製程加工，觀察沖剪面以評估第二相α相的分布型態與延性對成形性的影響。
擠型材經摩擦攪拌製程後可能殘留過飽和固溶狀態，FSP材可能因此有長時間自然時效現象；將FSP材進行安定化熱處理能有效縮短時效時間，並根據X-ray繞射峰2θ值於安定化熱處理後之偏移，推測安定化熱處理消除了過飽和固溶狀態。基地β相的硬度於安定化熱處理前後有明顯變化，可能因此造成FSP材與FSP-S材在拉伸性質與沖剪表面上的差異。
微觀組織方面，摩擦攪拌製程後SZ區中包含顆粒狀組織與網絡狀組織：網絡狀組織即α相分布在β相的晶粒中與晶界上，與文獻描述的析出型態相仿；顆粒狀組織則是由細小等軸的α 相分布在基地中。
將擠型材、FSP材及FSP-S材進行拉伸試驗，了解拉伸性質與破壞機制於改質前後的差異。甫經摩擦攪拌後的FSP材有較擠型材高的抗拉強度，但幾乎沒有延性，拉伸過程中缺陷可能形成在基地β相上；摩擦攪拌並安定化後的FSP-S材之拉伸性質則與擠型材相近，且破壞都起源於α相與α/β相界。
摩擦攪拌製程進行時，在熱影響區(HAZ)中的θ相與AlLi相可能於摩擦攪拌時分解進入基地，在安定化熱處理後θ相重新析出，因其析出強化效果較AlLi相佳，使得HAZ硬度上升，造成FSP-S材各區域硬度不均勻的現象。由於不均勻的硬度性質，在垂直摩擦攪拌進給方向的拉伸測試中，試片都斷裂在硬度較高、或是硬度不均勻之處。
沖剪面觀察的部分，在F材的沖剪面上發現平行擠型方向的裂紋，可能與板狀第二相有關；FSP材則可以發現由於β相的脆性而形成的缺陷；FSP-S材在沖剪後可獲得品質最佳的沖剪面，原因可能是屬於破壞起點的第二相在摩擦攪拌後細化了，且β相的脆性現象在安定化處理後有所改善。

Magnesium alloys have advantages such as low density, high specific strength and good mechanic damping properties. They are often applied for 3C and transportation industries as structural materials. Magnesium alloys with adding lithium element can make the density lower and the workability better than pure magnesium. A recent report suggested that the second phase α with plank-like shape in extruded dual-phase Mg-Li alloy might be the initial points of fracture under tensile test. In order to redistribute the second phase α, friction stir processing (FSP) followed by stabilization heat treatment is applied for trying to improve the mechanical properties of extruded Mg-9Li-2Al-1Zn alloy (LAZ921-F). This study focus on the effects of distribution of the second phase α on the tensile fracture characteristics and the effects of the ductility change on the roughness of blanking surfaces of Mg-9Li-2Al-1Zn alloy after FSP (LAZ921-FSP) and stabilization heat treatment (LAZ921-FSP-S).
According to the shifts of X-ray diffraction peaks, supersaturated solid solution induced by FSP may be eliminated after stabilization heat treatment. Stabilization heat treatment also makes aging time less. The β phase greatly affected by stabilization heat treatment may dominate the changes of tensile mechanical properties of LAZ921-FSP.
In the microstructure of FSPed LAZ921 magnesium alloys, there are two kinds of microstructures in SZ. The one is composed of equal-axed α particles. The other is composed of α phase on the grain boundaries of β phase and the α phase is dispersed in the matrix with needle-like shapes.
On tensile mechanical properties, the experimental results indicate that LAZ921-FSP has better strength and worse elongation than LAZ921-F. The initial points of fracture in LAZ921-FSP were located on β phase. LAZ921-FSP-S and LAZ921-F have similar tensile mechanical properties and similar initial points of fracture occurred within α phase and α/β interfaces.
The AlLi phase and θ phase in heat affected zone (HAZ) may be dissolved into matrix during FSP. Because that the θ phase re-precipitates after stabilization heat treatment and induces greater precipitation hardening effect than that induced by AlLi phase, the hardness of HAZ is higher than other zones affected by FSP. The fractures caused by tensile stress perpendicular to processing direction are on the zones with higher hardness and where hardness difference ocurr.
After blanking, there are cracks parallel to extrusion direction found in LAZ921-F. Also, there are cracks induced by blanking found in LAZ921-FSP due to the brittleness of β phase. The quality of blanking surfaces of LAZ921-FSP-S is better than LAZ921-F and LAZ921-FSP because of finer second phase α fined by FSP and better ductility improved by stabilization heat treatment.

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