Manufacture aluminum alloy tube from powder with a single-step extrusion via ShAPE
Introduction
Aluminum (Al) alloy powders with transition metal (TM) additions such as iron (Fe), titanium (Ti), chromium (Cr), and vanadium (V), referred to as Al-TM powders, demonstrate high mechanical, wear, and corrosion performance at operating conditions over wrought alloys [1], [2], [3], [4]. Their enhanced performance is typically attributed to the formation of uniformly distributed intermetallics comprised of Al-Fe-Cr-Ti which possess limited solid solubility and low diffusivity into the Al matrix at ambient and elevated temperatures [5]. Development of such formulations with targeted properties designed for medium to high strength applications is crucial for lightweighting and energy savings in several applications such as automotive, aerospace, military, and infrastructure. Powder metallurgy has been a preferred industrial route adopted for manufacturing components from powder feedstock. Industrial manufacturing requires powders to be consolidated, canned, degassed, pressed and finally formed into final parts. This method is a labor- and energy-intensive route for manufacturing components [6], [7]. There is a critical need for developing scalable, energy-efficient approaches that can effectively transform high performance powder feedstock into semi-finished and finished components.
Shear Assisted Processing and Extrusion (ShAPE) is a solid phase processing technique that deforms and extrudes starting material by thrusting a rotating die onto the precursors and generating high shear plastic deformation and heat. Recent work on friction extrusion [8], [9] showed that Al-TM rods could be manufactured in a single step. Whalen et al. showed that ShAPE Al-TM rods demonstrate a fine equiaxial grain structure [10], [11] with refined, uniformly distributed second-phase particles in the Al matrix [12], [13] and demonstrate simultaneously enhanced ultimate tensile strength and ductility. ShAPE is a preferred route over the traditional powder metallurgy approach for making Al-TM components owing to its ability to consolidate and extrude powders into solid rods in a single-step.
The objective of this study is to apply ShAPE as a method to fabricate thin-walled tubes from gas-atomized powders of Al-12.4TM alloy (Al with 12.4 wt% TMs). Previously, the only instance where ShAPE was used to fabricate tubes from disparate material feedstock successfully was using melt-spun AZ91 flakes [14]. On the other hand, ShAPE was used to manufacture ZK60 [15], [16], AA6063 [17], and AA7075 tubes [18] from solid billets successfully. High performance tubing has several applications in vehicles, buildings, and HVAC applications. Therefore, there is a benefit in developing manufacturing processes that can synthesize tubes from pre-alloyed aluminum powder precursors in an energy-efficient manner. In this work, ShAPE process parameters were explored to identify a manufacturing route that facilitates a single-step extrusion of Al-TM powders into tubes. To understand the powder-to-tube transformation, we examined the microstructure evolution of the tube and the remnant precursor. The density and hardness of the tubes were determined and correlated with both microstructure features and corresponding processing conditions. Finally, the energy requirement of the ShAPE process was estimated and collated with that of the traditional powder metallurgy approach to manufacture from powder precursor.
Section snippets
Precursor material
The feedstock powder, Al-12.4TM, contains Al with 12.4 wt% transition metals, including Ti, Cr, Mn, Mo, Fe, Si, and other additives. The pre-alloyed powder provided by Kymera International was produced by induction melting, followed by inert gas atomization, and screened to <400 μm. Powders were stored in an ambient environment and utilized as received in this study. The chemical composition of the pre-alloyed powders can be found in the previous work [8], [9].
ShAPE process
The process setup for ShAPE has
ShAPE tubes
The surface morphology of the tubes made with different feed rates is presented in Fig. 2. Because the machine extruded horizontally, gravity deflected the rotating extrudate and caused eccentric rotation. When the extrudates are long and the die advanced per revolution is low (die feed rates ≤20 mm/min), the scrolled undulation patterns are visible on the surfaces of the tubes. With a similar RPM and an increased feed rate, the undulation pitch increased while the tube also became straighter
Energy consumption calculation
We calculated the energy consumption of the ShAPE process from machine data. The energy consumption consists of two parts: (1) spindle energy and (2) tailstock ram energy.
Firstly, the spindle energy is determined by the integral of spindle power over time:
Secondly, the tailstock ram energy is calculated from the integral of the instantaneous ram force over distance s, as shown in the equation below:
Spindle power, time, tailstock force, and ram distance are
Conclusions
This study reports a method of directly extruding high-temperature aluminum alloy tube from powder via ShAPE, bypassing many complex steps used in traditional powder metallurgy and saving considerable energy and time. The integrity of the tubes is validated by microstructural inspection and density results. Material evolution from powder to solid tube is investigated and discussed with the deformation mechanism. Microstructure and hardness are correlated with extrusion speed. The main findings
Funding
PNNL is operated by Battelle Memorial Institute for the U.S. Department of Energy under contract DE-AC05-76RL01830. This work was sponsored by the U.S. Department of Energy Advanced Manufacturing Office. The authors would like to thank Scott Taysom and Md. Reza-E-Rabby for support on tooling and fixture design and Anthony Guzman for assistance in sample preparation.
Data availability statement
The raw and processed data required to reproduce these findings cannot currently be shared as a result of technical limitations and developing intellectual property.
Declaration of competing interest
The views and opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately
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