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Title: Effect of Processing Parameters on Microstructure and Mechanical Properties of Friction Stir Processed Aluminum Alloys
Other Titles: تأثير عوامل المعالجة باستخدام الخلط الاحتكاكي على البنية المجهرية للألمينيوم
Authors: Ali Hasan Hayati 
Supervisor: Dr. Khaled Al-Fadhalah
Keywords: mechanical engineering ; Processing Parameters; Microstructure; Friction;
Issue Date: 2016
Publisher:  Kuwait university - college of graduate studies
Abstract: Friction stir processing (FSP) has been recently utilized as an effective technique for microstructural modification and property enhancement of different metallic alloys. Typically, FSP produces fine equiaxed and homogeneous grains in the processed materials with an average grain size of 10 μm or less. FSP was originally developed based on the principle of friction stir welding (FSW) that had been alternatively used to join many metallic alloys, such as aluminum alloys, which are difficult to weld by conventional fusion welding methods. In this study, FSP has been applied to study the effect of processing parameters on the microstructure and mechanical properties of two aluminum alloys, i.e. commercially pure aluminum AA1050 and aluminum alloy AA6063. This has been achieved by conducting FSP with three different pin rotational speeds (600, 800 and 1200 rpm) and two different traverse speeds (50 and 150 mm/min). For AA1050, a wide and defect-free stir zone of basin shape has been formed for all FSP parameters used in this study. A stir-zone (SZ) of basin shape was also formed in AA6063. Yet, it was found that the use of high traverse speed of 150 mm/min introduced narrow SZ with pin-hole and/or tunnel type defects. Limited changes in grain refinement occurred in the SZ of AA1050, as the grain size ranges from 12 to 18 μm for all processing parameter. For AA6063, the SZ grain size has decreased with decreasing the rotational speed and increasing the traverse speed, achieving a minimum grain size of 2 μm by the use of 600 rpm and 150 mm/min. In addition, FSP of AA1050 resulted in a similar reduction in the microhardness at the SZ (~27 Hv) for all the process parameters, as compared to the base metal (45 Hv). Surprisingly, the reduction of microhardness in the SZ of AA6063 became less with increasing the rotational speed (39 to 58 Hv for processed materials and 76 Hv for base metal), which was correlated with the increase in re-precipitation of hardening particles. Compared to AA1050, the microstructural refinement and mechanical properties of AA6063 have been significantly affected by FSP parameters, influencing the thermal cycle of FSP and ultimately controlling the dynamic recrystallization and re-precipitation of hardening particles in the SZ. The current results indicate the combined use of 50 mm/min and 1200 rpm is most beneficial to optimize both the microstructure and mechanical properties of FSPed AA 6063 samples.
Appears in Programs:0630 Mechanical Engineering

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