Papers by Keyword: Rheo-Extrusion

Abstract: Twin screw rheo extrusion (TSRE) is a continuous semisolid forming process. The process takes advantage of the thixotropic properties of semisolid metal slurry and the high shear, controllable forward driving and self-sweeping capabilities of a counter rotating twin screw mechanism, offering a one-step melt-to-product forming technology with significant savings on energy consumption and manufacturing cost. The present work was carried out to investigate the feasibility of the process for processing light alloys using an AZ91D magnesium alloy and to obtain optimized operation conditions for microstructure control. A range of processing parameters was tested for slurry making, feeding and extrusion and their effect on microstructure development was examined. Experimental results showed that slurry with non-dendritic primary phase particles of various volume fractions, typical of semisolid microstructure, was obtained prior to extrusion. The particles were further refined during extrusion due to dynamic shearing applied by the twin screw mechanism under controlled thermal schemes and the final microstructure obtained after extrusion was dominated by uniformly distributed equiaxed, non-dendritic spherical grains and the average grain size was in the range of 35-80 mm, depending on processing parameters. This paper presents the performance of the TSRE process, focussing on process optimization and microstructure control. Mechanisms of microstructural refinement and particle morphology evolution are discussed.

Abstract: In this paper, effects of technical parameters on process stability and microstructure during continuous rheo-extrusion process of 6201 alloy wire were investigated. The optimal process parameters for producing 6201 alloy wire are obtained. The casting temperature is from 720°C to 740°C, and the roll rotating speed is 15r/min. The 6201 alloy wire with good performance has been successfully manufactured. After heat treatment, the tensile strength of the product reaches 325 MPa and the resistivity reaches 32.47 nΩm, which is better than LHA2 conducting wire of China.

Abstract: Rheo-extrusion of hypereutectic Al-14.8%Si-4.5%Cu-1.1%Mg (in mass%) alloy which is considerably difficult to hot-extrude was tried using semi-solid slurry with fine solid granules and almost finely dispersed primary Si particles, made by a newly developed rotor process. Trials of rheo-extrusion at the constant extrusion ratio of 36 using this semi-solid slurry were carried out at the different conditions of the extrusion temperature and the ram speeds ranging from 520 to 560oC and from 5 to 20mm/s, respectively. Under the all rheo-extrusion conditions, this semi-solid slurry could easily be rheo-extruded to the round bars of 6mm diameter with sound surface at much lower extrusion force than that of hot-extrusion at very low extrusion ratio. In addition, the characteristic age-hardening behavior which is thought to be essential for the rheo-extrusion process has been found out, namely the peak hardness values of aged bars rheo-extruded at 520 and 540oC were considerably higher, 30HV at maximum, than that of a gravity casting.

Abstract: A new rheo-extrusion technique has been developed to produce extruded profiles. The AZ31 slurry is fabricated by a twin-screw mechanism, and has spheroidal solid particles with a grain size of about 50 to 80μm. The slurry was introduced into an extrusion container with an inner diameter of 95mm, and then squeezed to a billet before extruding into a round bar with a diameter of 22mm using a 500kN extrusion machine. It is found that the new technique has a lower deformation resistance than that of the conventionally hot extrusion technique in the same extrusion velocity. The microstructure and mechanical properties of the rheo-extruded bars were examined in detail. The results illustrated that grains of the bar were very fine with the average grain size about 2.3μm，and the mechanical properties were improved substantially compared with those of the same alloy produced by the conventional hot extrusion.

Abstract: Rheo-extrusions of A7075 aluminum alloy were carried out utilizing semi-solid slurries with different solid granule sizes, which were made by a simple method combined a thin upright tube with a water-cooled tube. Every structure of slurries was granular and average solid granule sizes could be controlled by 0.05 to 0.11mm. These slurries were extruded to round bars at extrusion ratio of 36 and press ram speed of 10mm/s mainly, just after cooling to 833K ( fs > 0.9 ). All of the slurries could easily be extruded to bars with smooth surfaces at much low extrusion forces than those of hot-extrusions. Tensile strength of rheo-extruded bars after solution treatment increased with decreasing of the solid granule size. Peak hardness level at T6 condition equivalent to that of hot-extrusion could be obtained at the finest solid granule size.

Abstract: Semi-solid slurry of A7075 aluminum alloy with fine solid granules was tried simply to make by passing the melt through upright tube followed by inclined water-cooled tube. Structures of solidified slurries were granular and mean grain sizes of about 0.06 to 0.11mm could be obtained. When the slurries introduced into an extrusion container kept at semi-solid temperature 873K were extruded to round bars at various extrusion ratios and press ram speed of 10mm/s, just after cooling to 833K, they could easily be extruded to bars with smooth surfaces at lower forces. Although every tensile strength of extruded bars were lower than that of hot-extruded one, there was a tendency that finer the solid granules in slurry, higher the tensile strength of extruded bar.

Abstract: In order to extrude A7075 aluminum alloy soundly from melt without using feed stock billet, rheo-extrusion was tried by utilizing semi-solid slurry with fine solid granules made by employing cooling tube. When the melt moving down inside thin tube was adequately cooled in different ways and introduced into an extrusion container kept at semi-solid temperature of 873K, structure of solidified slurries were granular and mean grain sizes of about 60 to 120μm could be obtained. Subsequently, these slurries were extruded to round bars at various extrusion ratios (28 to 64) and press ram speed of 10mm/s, just after cooling to 833K. The newly developed slurries could easily be extruded to bars with smooth surfaces at lower forces. Although every tensile strength of extruded bars were lower than that of hot-extruded one, there was a tendency that finer the solid granules in slurry, higher the tensile strength of extruded bar.