An Experimental Investigation on the Mechanical Properties of a Laminated Magnesium Part fabricated Using Repeated Lateral Extrusion (RLE) technique

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: An Experimental Investigation on the Mechanical Properties of a Laminated Magnesium Part fabricated Using Repeated Lateral Extrusion (RLE) technique

ارائه دهنده: Provider: Ali Mehdinezhadiani

اساتید راهنما: Supervisors: DR. Fereshteh Saniee

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr. Mahmudi, Dr. Shaban

زمان و تاریخ ارائه: Time and date of presentation: 2023-9-25

مکان ارائه: Place of presentation: Seminar 3

چکیده: Abstract: During past two decades, various Sever Plastic Deformation (SPD) processes have been used to refine the microstructure of different metals and alloys. ECAP (Equal Channel Angular Pressing) and its alternative NECAP (Non-Equal Channel Angular Pressing) are two of these SPD techniques, usually employed for bars and rods. The NECAP process, with an extrusion ratio higher than unity, leads to larger plastic strains and more grain refining during the first pass, compared with the ECAP. On the other hand, magnesium and its alloys possess various benefits such as low density, high strength to weight ratio and biocompatibility. However, simultaneous improvement of the strength and ductility of magnesium alloys is a challenge, which can relatively be overcome employing SDP methods. So far, the equal channel angular pressing process has mainly been used to modify the microstructure, and limited research has been done for making layered laminate using this process. In this study, the process of non-equal channel angular pressing, which has previously been utilized just for production of fine-grained materials, is used to produce laminates consisting of two similar layers of AZ91 magnesium alloy. To attain this goal, the AZ91 alloy is processed at temperatures of 350ºC and 400ºC, with two different ram speeds and up to two passes, employing the NECAP method with an extrusion ratio of 2. Besides various mechanical properties, the characteristics of the microstructure and bonding properties between the layers of the NECAP products have comprehensively been studied. Moreover, the force-displacement curve is examined for all the process conditions and the effects of different parameters on the required forming force are examined. It was found that the temperature of the process and the number of passes had significant influences on the homogeneity of the microstructure, yield and ultimate strengths, ductility and microhardness of the NECAP product. The compression test along the normal direction (ND) showed that in the second pass, the bonding effect is more pronounced than the modification of the microstructure. Microstructural studies showed that the lowest grain size obtained after the first and second passes were respectively 11.9μm and 8.4μm, indicating significant grain refinements in comparison with the as cast component. Both the strength and microhardness of AZ91 Mg alloy increased after the first and second passes, but ductility decreased after the second pass, under the influence of the bonding between two layers. After the first pass at low temperature and ram speed, a bi-modal microstructure was observed in the deformed part. In addition, the examination of the strength of the bonding between the layers showed that the higher process temperature and lower strain rate resulted in a higher uniformity and strength of the inter-layer bonding. Various experimental findings implied that conducting the NECAP process up to two passes at temperature of 400 oC with a ram speed of 1 mm/min would result in the best combination of mechanical properties and bonding strength

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