本研究採用Al-Si-Mg系合金4008，分別經過不同熱處理後進行摩擦攪拌製程。熱處理條件分別為完全退火（O材）以及固溶化處理後進行人工時效至峰值（T6材）。之後針對攪拌區(SZ)的顯微結構進行解析，並探討摩擦攪拌製程對於機械性質的影響。而本實驗同時進行接合的研究，結果發現接合後原先界面處不再存在，且材料受力後弱化之起點發生於接合處以外。

　　根據實驗結果顯示，不同前熱處理試片（O材及T6材）在摩擦攪拌過後，SZ的微觀組織並無顯著差異。矽晶均更為破碎，並有部份圓鈍化的現象，且較攪拌前均勻散布於α-Al基地。攪拌前矽晶之長軸及短軸分別約26μm及5μm，在攪拌過後則分別減少至11μm以及4μm。觀察α-Al基地時發現有動態再結晶的現象，其晶粒呈等軸貌，晶粒徑經攪拌後由約36μm細化至約11μm。從T6材之X-ray繞射圖形發現，攪拌後SZ的TD面會產生傾向於（220）之從優取向。此外本研究並觀察摩擦攪拌對自然時效的影響，發現不同熱處理的試片經摩擦攪拌過後，有著相似的自然時效曲線，均在四天後曲線趨於平緩。

　　綜合以上所述，可推測摩擦攪拌製程能相當程度地消除前熱處理對微觀組織的影響。

　　T6材之SZ在攪拌過後發現降伏強度從306MPa下降至166Mpa。雖然攪拌使SZ的晶粒較細化，但其拉伸變形阻抗卻下降，研判為攪拌過程中的高溫與高應變狀態使得析出強化相Mg2Si重溶，而降低強化之效果，導致材料軟化。

　　本研究在高溫的拉伸測試中，發現O材（OB）及其經過攪拌的材料（OF）其高溫變形阻抗在300℃附近發生陡降的現象，並且在300℃以前，OF之UE均小於OB。而在400℃及500℃時，OF具有相當高之延性。

　The Al-Si-Mg 4008 alloy which had been experienced O and T6 heat treatment respectively was selected for FSP in the present study. Subsequently, examined the microstructure in the stir zone and correlated mechanical properties changing with FSP effect. There was no obviously interface could be seen and with better properties in the joint by FSW.

　Observation displayed that the microstructure in the SZ were similar irrespective of heat treatments. The Si particles were broken into finer ones and dispensed homogeneously partial in α-Al matrix. The longitudinal size and transverse size of Si particles were 26μm and 5μm before being stirred and were decreased to 11μm and 4μm after being stirred. The α-Al matrix was composed of equiaxed grains arose from dynamically recrystallization and grain size decrease indeed to some extent, i.e. from original 36μm to final 11μm. The XRD demonstrated that the transverse plane was preponderantly coincident with crystallographic (220) plane. By the way, we observed that both samples with different heat treatments exhibited similar behavior of natural aging which went steady in four days after FSP. As all mentioned above, it is reasonable to deduce that FSP could eliminate the microstructure resulted from different pre-heat treatment apparently.

　The yield strength in the SZ of T6 sample deteriorated drastically from 306MPa to 166MPa despite of fine microstructure. The softened phenomenon may be ascribed to remelted of strengthening Mg2Si precipitates.

　When tensile test was carried out in high temperature surrounding, the tensile strength of OF metal declined severely at 300℃. The uniform elongations of OF are lower than that of OB before 300℃. On the other hand, OF presented high ductility at 400℃ as well as 500 ℃respectively.

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