- 學位論文
α/β雙相鎂鋰合金織構及摩擦攪拌改質效應對拉伸機械性質影響之研究
Effects of Texture and Friction Stir Processing on the Tensile Mechanical Properties of α/β Dual-Phase Mg-Li Alloy
摘要
鎂金屬及其合金是結構用金屬材料中比重最輕者，其輕量、高比強度、制震性佳及電磁波遮蔽效應等特色可以使其在多種的領域中獲的極大的應用。本研究係利用一摩擦攪拌製程(Friction Stir Process, FSP)來對鎂鋰合金進行改質，然而目前對於LZ系列鎂鋰合金經攪拌製程改質之相關研究甚微，因此本實驗採用擠型之雙相型鎂鋰合金(LZ91-F)來作為研究對象，探討雙相型LZ91鎂鋰合金之織構及其機械性質之FSP改質效應。本研究發現LZ91-F經過摩擦攪拌改質後，攪拌區之硬度獲得提升，且沿攪拌方向之攪拌區拉伸強度也獲得提升，另外針對擠型材做不同方向角以及應變速率之拉伸試驗來探討鎂鋰合金擠型材之織構效應。從金相觀察中得知富鎂α相在其母相富鋰β相中有被固溶、分散之現象；且α相在其母相β相晶粒中有一優選方位之網格析出，。從XRD發現原始擠形材有擠型織構產生，但經過FSP後均受到破壞，原始織構所具有之繞射峰強度經過FSP後均下降或是繞射峰消失。另外透過極圖繞射發現α、β兩相在擠型時之晶體學位置關係，也證實擠型材之拉伸試驗結果與擠型織構有密切關係。透過EBSD背向電子繞射進一步確認時效之針棒狀α相與其連續相β相晶粒內部之析出方位與晶面關係。
並列摘要
Magnesium and its alloy is the lightest structural use metal. It’s light weighted、high specific strength、shock absorption and electromagnetic shielding effect makes it widely used in many area. In this research we use a “Friction Stir Process, FSP” to reform the magnesium alloy. So far the researcher has mainly focused on AZ series magnesium alloy, but less in the LZ series. During the experiment we choose extrusion formed dual phase magnesium-lithium alloy (ASTM LZ91-F) as our target, discussing the internal preferred orientation and mechanical properties after FSP. Compared to the extrusion materials we’ve found out that after FSP the hardness of the stir zone has increased, and the tensile tests along extrusion direction has increased. Also different tensile parameters was introduced to reveal the properties of extruded materials. In the metallographic observation that the α-phase of FSPed specimen was solid-soluted and distributed into β-phase and α-phase was precipitated as a rod-like shape、mesh structure in β- phase grain. In XRD experiment we’ve discovered that extrusion specimen had a extruded texture, but diminished or disappeared after FSP. Pole-Figure was carry out to reveal the crystallographic orientation of the extruded specimen. It proved that the tensile test result would affect by texture. EBSD was introduced to find out the crystallographic relationship between rod-like α-phase and β-phase grain.