الفهرس 
Engineering Materials
Visual and Metalographic ResultsOnly 14 pages are availabe for public view
 |  | from | 110 |  |  |
| | | from | 110 | | |
Abstract
Super light materials with high mechanical and thermal properties become a critical need in modern industries. Aerospace, automotive, trains and other many industries use Metal Matrix Composites to fulfill this need.
Friction Stir welding (FSW) as a solid state welding process has been used since its introduction in 1991 by TWI of England to weld the super lightweight materials in NASA space shuttle tanks. Friction stir processing (FSP) was developed based on the same principles of FSW mainly to enhance the surface properties of various materials and to produce surface composites.
Surface metal matrix composites of AA7075-T1 and T6 as the metal matrix were developed using FSP. Two ceramic particle types were used for reinforcement of surface composite, micro sized Al2O3 particles and ultra-fine SiO2 particles. A groove of 3 mm depth and 1.2 mm width was machined on the surface of AA7075 to provide the highest reinforcement volume fraction on the produced surface composites. FSP tool used was made from tool steel having 20 mm shoulder diameter, 3.5 mm pin length and 7 mm pin width. Tool pin profile of square and cylindrical was designed and manufactured to produce FSP specimens. The tool had a concave shoulder and tapered bottom pin. The FSP parameters used were rotation rate of 600 rpm and traverse speed of 50 mm/min. The tool was heat treated to both HRC 45 and 60 before FSP. The previous mentioned experiments was conducted on friction welding machine at the friction stir welding and processing laboratory at Suez University. Preliminary experiments was conducted to evaluate other workshops machine suitability for the process. Number of variable have been changed, tool design, rotational speed, traverse speed, tool penetration procedure and groove dimensions were also studied.
The developed surface composites were evaluated using different metallographic techniques to investigate the macro and micro features. The hardness profile was also measured across the processed zone.
The surface composite hardness was improved by 10-30% compared to the unreinforced alloy. The tool with the above mentioned dimensions enables obtaining sound surface without any visible defects. Squared tool pin profile enhanced reinforcement particle distribution. Moreover, number of processing passes effect on surface composite was evaluated. The surface composites achieved by three consecutive passes of processing showed uniform particle distribution on the surface. The hardness and the microstructure of surface metal matrix composite have been investigated. Many parameters can influence the properties of such surface composites the current results are compared with those from other similar composites reported in the literature.