ORIGINAL ARTICLE Hydrostatic radial forward tube extrusion as a new plastic deformation method for producing seamless tubes S. S. Jamali 1 & G. Faraji 1 & K. Abrinia 1 Received: 29 December 2015 /Accepted: 7 April 2016 # Springer-Verlag London 2016 Abstract Hydrostatic radial forward tube extrusion (HRFTE) as a new and innovative method is developed for producing large-diameter seamless tubes from smaller hollow billets. The HRFTE process is based on hydrostatic pressure, and radial forward tube extrusion provides the possibility of pro- ducing a large-diameter tube with low hydraulic oil pressures. In this procedure, a movable punch placed inside the hollow billet plays the main role in reducing the required hydrostatic pressure. The HRFTE process was applied to pure aluminum at room temperature, and the mechanical properties, material flow behavior, and microstructural evolution were examined. Since the large effective strains were applied to the material during the process, the strength and hardness were significant- ly improved. Yield and ultimate strength were increased, re- spectively, about 2.48 and 1.86 times compared to the initial values. Microhardness was also increased to 59 Hv from the initial value of 28 HV. Good homogeneity of effective strain and microhardness in the longitudinal section was observed, but there is an inhomogeneity along the tube thickness. The HRFTE process seems to be an extrusion process with a high capability of industrialization for producing a large-diameter seamless tube with superior mechanical properties using low hydrostatic pressures. Keywords Radial forward extrusion . Hydrostatic pressure . Mechanical properties . Aluminum . Effective strain 1 Introduction In the production of industrial parts using metal-forming pro- cesses, extrusion is one of the most important methods. Considering the directions of the material flow and punch movement, extrusion processes are divided into three catego- ries of forward (direct), backward (indirect), and radial (lateral) extrusion. The combination of two or three of these processes is named as a combined extrusion method. Some methods of combined extrusion are double backward extru- sion [1], backward forward extrusion [2], radial backward extrusion [3], and radial forward extrusion [4]. Hydrostatic extrusion, patented by Robertson in 1893 [5], has several ad- vantages over conventional extrusion including almost no friction, lower process load, better surface quality, and higher hydrostatic compressive stress (essential for processing hard- to-deform materials) [6]. Bridgman in 1952 carried out several experiments in the design and construction of the pressure chamber which is an important part of the system [7]. Among the extrusion products, seamless tubes are used extensively in different industries. Production of the seamless tubes is conventionally performed by using piercing forward extrusion, backward extrusion [8], and port-hole methods [9]. During the last decade, several tube severe plastic deformation (SPD) methods with applying intense plastic strain leading to significant grain refinement were invented for improving the mechanical properties of the tubular-shaped metals [10–12]. Faraji et al. [13, 14] introduced tubular channel angular press- ing (TCAP) [15] and parallel tubular channel angular pressing (PTCAP) processes for producing ultra-fine-grained (UFG) tubes. Babaei et al. developed tube cyclic expansion extrusion (TCEE) [16]. These processes may be used only for small tubes on the laboratory scale [17]. Whereas the long and large tubes are demanded in industries, development of effective methods is necessary. Scaling up of the available SPD process * G. Faraji ghfaraji@ut.ac.ir 1 School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran 11155-4563, Iran Int J Adv Manuf Technol DOI 10.1007/s00170-016-8754-6