A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 1 9 Extruded shapes are often ideal for long aircraft components that require consistent cross sections throughout the length of the part[1]. The most common aerospace extrusions include seat tracks produced using the workhorse titanium alloy, Ti-6Al-4V (Ti-64). However, major advancements have occurred in the use of extruded titanium shapes deployed in a variety of other applications. Uses range from specialized parts in subsonic systems to components in unmanned submarines that take advantage of titanium’s favorable strength-to-density relation- ship and superior corrosion resistance. Billet temperatures used in the extru- sion of titanium alloy shapes are typically above the beta transus temperature of the material, and the reduction ratios are higher than those used in other product types. Gross titanium extrusion, while producing radical savings in materials due to closer shape approximation, also requires less machining to achieve the finished product. In an effort to further reduce overall manufacturing costs and improve the buy-to-fly ratio, the R&D division of Plymouth Engineered Shapes (PES) has successfully developed an innovative process and manufactured near net shape Ti-64 extrusions, roughly 30 ft long, on a production scale that includes various geometries. This article presents different near net shapes extruded at PES and provides the mechanical properties, microstructures, and dimensional tolerances consistent throughout the full length of the extrusion. METAL EXTRUSION The metal extrusion process can be broadly classified into two main categories—direct and indirect[2]. In the process described here, the direct or forward extrusion process was employed, where the die and ram are on opposite ends and the billet travels in the same direction as the ram (Fig. 1). Typically, the cross section of the work billet is much larger than the cross section of the extruded part. To relate the cross section of the workpiece to that of the extruded product, a value commonly called the extrusion ratio was established, which is defined as the ratio of the area of the original billet cross section (Ao) to that of the extruded product (Af). The extrusion ratio, or reduction ratio, can be expressed as (Ao/Af). Depending on final part geometry, a wide range of extrusion ratios for extruding different titanium products is available. Typically, most titanium extrusion presses are water hydraulic systems with remarkably high strain rates in the range of 10 s-1 or higher[3]. A beta extruded titanium billet will yield products with an elongated grain structure that is often recrystallized by hot stretch straightening and annealing. The resultant structure consists of recrystallized prior beta grains with colony alpha, which offers an excellent combination of strength, fracture toughness, and fatigue life[4]. MATERIALS AND PROCESSING Ti-64 billets, with nominal composition per AMS 4935[5] ranging from 6.0 to 9.25 in. in diameter, were induction heated to a temperature above the beta transus and extruded into two distinct geometric profiles. These two shapes were selected for their uniqueness in terms of geometry and application (Fig. 2). While the “T profile” is often used for aerospace structural components, the shape with more complex ADVANCEMENTS IN NEAR NET SHAPE EXTRUSION FOR AEROSPACE APPLICATIONS The aerospace industry could benefit from recent progress in making near net shape titanium extrusions for applications beyond the long structural components of an aircraft. Phani P. Gudipati* and Michael B. Campbell Plymouth Engineered Shapes, Hopkinsville, Kentucky *Member of ASM International Fig. 1 — Forward extrusion process where the ram pushes the hot metal through the die.
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