Development of aluminum rheo-extrusion process using semi-solid slurry at low solid fraction T. RATTANOCHAIKUL 1 , S. JANUDOM 1 , N. MEMONGKOL 2 , J. WANNASIN 1 1. Department of Mining and Materials Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla, 90112, Thailand; 2. Department of Industrial Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla, 90112, Thailand Received 13 May 2010; accepted 20 June 2010 Abstract: An aluminum extrusion process is mainly used to fabricate long tubes, beams and rods for various applications. However, this process has a high production cost due to the need for investment of high-pressure machinery. The objective of this work is to develop a new semi-solid extrusion process using semi-solid slurry at low solid fractions. A laboratory extrusion system was used to fabricate aluminum rods with the diameter of 12 mm. The semi-solid metal process used in this study was the gas induced semi-solid (GISS) technique. To study the feasibility of the GISS extrusion process, the effects of extrusion parameters such as plunger speed and solid fraction on the extrudability, microstructure, and mechanical properties of extruded samples were investigated. The results show that the plunger speed and solid fraction of the semi-solid metal need to be carefully controlled to produce complete extruded parts. Key words: aluminum alloys; extrusion; semi-solid metal; rheo-extrusion; gas induced semi-solid (GISS) 1 Introduction Extrusion is one of the various forming processes that is used to produce long and straight metal products with constant cross section, such as bars, solid and hollow sections, tubes, and wires[1]. In extrusion process, a billet is heated and forced through a die orifice. The products from this extrusion process are in a near net shape. However, the extrusion process requires a high-pressure machine to force the metal in the solid state. In addition, defects such as surface cracking, oxide inclusion and piping defect can be found in the products of an extrusion process[2]. An alternative way to reduce these process limitations is to apply a semi-solid extrusion process because it has several advantages such as the requirements of low extrusion force, good flowability, and less friction between the dies and the materials[3]. During the past several years, thixo-extrusion has been continuously developed since it is found to be able to achieve high quality products, for example, good surface finish and high ultimate tensile strength[4−10]. However, in a thixo-extrusion process, it is necessary to use a billet so only certain types of alloys can be processed and the scrap cannot be recycled on site[11]. From these restrictions, many research teams are focusing on the rheo-extrusion approach[12−16]. In previous studies on a rheo-extrusion process, FAN et al[12−13] performed experiments with twin screw rheo extrusion (TSRE) for magnesium alloys. The solid fractions produced in their work were more than 30% and the sleeve was kept at a high temperature of 630 °C and plunger speed was about 1 cm/s. The samples had uniform microstructure and quite high tensile strengths. LEE et al[14] investigated the behavior of melt extrusion for Al-Cu alloys. In the process, the molten Al-Cu alloy was held in a shot sleeve until the solid fraction was 78%. The slurry with the high solid fraction was then forced through the opening die at the plunger speed between 0.2 and 1.1 cm/s. The extrusion die was also kept at high temperatures of 500−520 °C. They reported that the high temperature of the die caused segregation of liquid phase. The way to solve this problem was to use lower die temperatures or to add some grain refiners. In summary, from Refs.[12−14], most of the rheo- Corresponding author: J. WANNASIN; Tel: +66-74-287-312; E-mail: jessada.w@psu.ac.th, jessada@alum.mit.edu DOI: 10.1016/S1003-6326(09)60371-X