Fundamental Research On Extrusion Forming Of Aluminum-tungsten Alloy Powder Rod

Aluminum and its alloys are characterized by their favorable comprehensive properties such as low density, good appearance and corrosion resistance, which have been extensively applied in different fields of marine, aviation and automotive industry. However, with the progress of science and technology, the national defense development and the improvement of people’s living standards, aluminum alloys are experiencing an increasing demand to obtain higher mechanical properties at room temperature and maintain reliability at elevated temperature, including the desired performances of wear-resisting, corrosion resistance, resistance to fatigue, etc. As a novel type of structure material, aluminum-tungsten alloy possesses the combination advantages of tungsten and aluminum. Therefore, such alloys have great application potential. More importantly, aluminum-tungsten alloy is quite possible to become a new generation of armor materials and aerospace engine structure materials due to its superior performance. Forming of aluminum-tungsten alloy power is a key issue for aluminum-tungsten alloy industrialization needed to solve.In this article, a process that aluminum-tungsten ultra solid solution alloy powder is formed by room temperature pressing, elevated temperature pressing and extrusion after secondary heating was firstly adopted. And the extrusion molding theoretical for aluminum-tungsten alloy rod is studied. It provides a theoretical basis to lay down plastic forming process of aluminum-tungsten alloy powder.The quality of alloy powder is a key factor affecting the density of the compacted body, and to a certain extent, affecting the final structure and properties of parts. Aluminum-tungsten alloy powder is analyzed in this paper by means of plasma emission spectrometer, field emission scanning electron microscopy. The results show that the aluminum-tungsten alloy powder belongs to high purity micron powder and obtains good formability and poor compression due to lower bulk density. It provides a reference for the selection of compacting pressure.On the basis of theoretical analysis of the powder compaction, the powder billet rod possess low cost and appropriate density is made through die design and process parameter optimization of room temperature pressing and elevated temperature pressing. By measure, the relative density is reached 0.943, and the hardness is reached 23.9HRB of the billets pressed.Aluminum-tungsten alloy was analyzed in this paper by means of isothermal compression, optical microscopy, scanning electron microscopy, hardness testing. Firstly, the deformation behavior of the alloy with different deformation parameters was systematically studied, and the constitutive model of the alloy under the different stress states was established. Secondly, the constitutive relationship model for this alloy was successfully developed using BP neural network. In the proposed model, the input variables are strain, strain rate and deformation temperature while the flow stress is the output variable. The results show that absolute maximum error between predicted and experimental values of flow stress is less than 10 Mpa, the correlation coefficient is 0.997. It was found that the established constitutive relationship model could provide a good representation of the test data and describe the whole deforming process better compared with the traditional method. Finally, based on the dynamic material model, the aluminum-tungsten’s two-dimension processing map was created, which showed that the alloy has three peak energy dissipation areas:(1) 450 ℃ ~480 ℃, 0.001s-1,(2) 490 ℃ ~520 ℃, 0.1s-1,(3) 530 ℃ ~570 ℃, 0.001s-1~0.1s-1. According to the actual production situation, the optimized choice of process parameters was within temperature 530℃~570℃ and strain rate 0.01s-1~0.1s-1. This provides the reference for choosing the forming parameters.Extrusion experiment was carried out at different temperatures and extrusion ratio to study the effect of extrusion parameters on organization and performance of aluminum-tungsten alloy rod in this paper. Results showed that:(1) density: fluidity of powder was improved with extrusion temperature increasing, and this was beneficial to fill voids between particles. Volume deformation and plastic deformation were promoted with extrusion ratio increasing, and this was beneficial to eliminate voids between blanks. Therefore, density was improved with high temperature and large extrusion ratio, and this verified the correctness of compression test of hot pressing billet.(2) microstructure: dynamic recrystallization was observed during extrusion process with extrusion temperature increasing, and this made grain refinement. Deformation degree was increased with large extrusion ratio, and this made deformation streamline detailed and grain refinement. Therefore, as-extruded Al-W alloy with minimum average grain size less than 5μm was obtained when the extrusion temperature was 540℃ and extrusion ratio was 35.(3) mechanical properties: due to dynamic recrystallization during extrusion process, optimal mechanical properties of as-extruded Al-W alloy was obtained when the extrusion temperature was 540℃ and extrusion ratio was 35. By measure, the hardness is reached 85.2HRB, the tensile strength is reached 479 MPa, and the elongation is reached 15.7%.Researches on plastic forming of aluminum-tungsten alloy power have not been reported home and abroad at present. In this paper plastic, forming theory of Al-W alloy creatively is studied, and this has great significance on industrialization development and application of aluminum-tungsten alloy. Meanwhile, Al-W alloy which is obtained by cold pressing, hot pressing and hot extrusion process has high desity and excellent mechanical properties, and this establish the base for widely used of Al-W alloy.