Papers by Keyword: Spray Forming

Abstract: The 8009 aluminum alloys were fabricated by spray forming and extrusion process. The microstructure and properties of the alloy were investigated by means of metallographic, scanning electron microscope and tensile test. The results indicate that at room temperature, the tensile strength of the extruded alloys can reach 415MPa, the yield strength 345MPa, elongation 22.5%. The tensile strength and yield strength of the alloys decrease with the increasing temperature, the plastic of alloys shows a down-up medium temperature brittleness law.

Abstract: 50Si-50Al alloys were synthesized by the Spray Forming process, and were further deformed in the semi-solid state. The spray-formed microstructure consists of small equiaxed primary Si in 3-5 μm scale. For semi-solid deformation at 650°C at solid fraction (fs) of 0.4, the stress increases initially to reach the peak stress, then decreases to a plateau level, followed by last stage of stress climbing, and the effects of the deformation speeds on the stress level are significant, but not large. For deformation at 750°Cat fs of 0.31, the stress increases initially, then increases at a slower rate, followed by last stage of fast climbing, and the lower the deformation speed is, the higher the deformation stress. The average deformation stress needed at 650 °C was much higher that that needed at 750 °C. The deformation was inhomogeneous at 650°C to become pieces of connected semi-solid clusters, while the deformation was much more homogeneous at 750°C.

Abstract: In the spray forming process, the atomizing quality is not very good under the low pressure. This article attempts to improve the quality of atomization through heating the gas. A mathematical model is built and calculated according to the existing knowledge, and then the influence of airflow temperature in the spray forming is theoretical calculated and analyzed. The experimental results show that the average grain size is 54μm when the gas is not heated; the average grain size is 39 μm which decreases by 27.7% than airflow unheated when the gas is heated to 150 °C. The calculation results show that when the gas is not heated, the first time atomization grain size is 201 μm, the second time atomization grain size is 15 μm, the total atomization time is 92 μs. And the velocity of atomization droplets is 80 m/s; when the airflow temperature is 150°C, the above results are 131 μm, 10 μm, 76 μs and 127 m/s respectively, the atomization quality has a certain improvement compared to the unheated condition. At the same time, the grain shape becomes more round as the temperature of airflow increases, and the holes between the grains also become smaller.

Abstract: In this paper, the Al-8.5Fe-1.3V-1.7Si alloys were fabricated by spray forming and extrusion process. The microstructure and mechanical properties of the alloy were investigated by means of metallographic, scanning electron microscope and tensile test. The results indicate that the tensile strength of the extrued alloys can reach 353MPa, the yield strength 300MPa, elongation 19.12%, at room temperature. At 250°C, the tensile strength of the extrued alloys can reach 221MPa, the yield strength 208MPa, elongation 13.33%.

Abstract: Al-22Si-5Fe-4Mn-3Cu-1Mg alloy billet was prepared by spray forming processing, and the morphology and microstructure development of the over-spray powder were investigated in this paper. The results show that the diameter of the most powder was about 38um. With the decreasing of the powder size, its shape became more round and surface more smooth. Heterogeneous nucleation was the main nucleation way and the microstructures were dendrite grains for the most of over-spray powder. The formation mechanisms of the different microstructures were investigated through comparison with the microstructure of the spray formed ingot.

Abstract: Working conditions, failure forms and property requirements of cold working die steels were presented. This review attempted to introduce the development of cold working die steels, the ways to improve its quality, heat treatment and surface treatment technology at home and abroad. Meanwhile, the characteristic and application prospects of spray-formed cold working die steels were analyzed.

Abstract: The T15 high speed steel (HSS) spray formed (SF) billets were manufactured using a twin-atomizer spray forming facility at Beijing Institute of Aeronautical Materials (BIAM) AVIC, China. The billets were then hot isostatically pressed (HIP) following hot forge (HF) and heat treatment (HT). The as-spray formed billet is integrally dense and has a high relative density of >98%, and the macrostructure is free of macrosegregation. The microstructure consists of polygonal grains of 20µm with tempered martensite inside the grains and refined carbides uniformly distributed along the grain boundaries. Hardness and three-point bending properties were also measured. The spray formed materials was comparable to those made by powder metallurgy in terms of microstructure uniformity, hardness and bending property.

Abstract: The hot deformation behaviors of spray formed superalloy GH738 were investigated by using of Gleeble-3500 simulator in the temperature range of 950~1200, with a strain rate of 0.13~6.5s^-1 and reduction of 50%. The corresponding flow curves were determined and hot deformed microstructures were observed. The results showed that the flow stress decreased with increasing deformation temperature or decreasing strain rate. A full dynamic recrystallization microstructures with fine-equiaxed grains were obtained at the temperature of 1100~1150 and strain rate of 2.6~6.5s^-1. The hot deformation activation energy Q was 580.81kJ.mol^-1, and the constitutive equation was derived by means of linear regression.

Abstract: Low-cycle fatigue (LCF) fracture of the spray formed GH738 alloy was investigated under total strain controlled mode at 650°C. Basic theory for evaluating fatigue lives by fatigue striations has been introduced. The crack length a and the crack propagation rate da/dN were measured and the curve of da/dN in crack propagation zone was obtained with Paris formula and tabulation trapezoidal formula, respectively. The size and symmetry of rapid fracture zone of fatigue were also studied. The results showed that the relationship of a and N was linear with tabulation trapezoidal formula, and the da/dN and a was conic with Paris formula. At last, quantitative analysis of fatigue fracture was also discussed.

Abstract: The microstructures and hardness of spray-formed and aged H13 steel were investigated by OM, SEM, XRD and hardness tester. Compared to the as-cast H13 steel, the microstructures of the spray-formed H13 steel is characterized by lower bainite, martensite and much more retained austenite, inducing lower hardness than the as-cast H13. The peak aging temperature for the spray-formed H13 steel is 50°C higher than the commercial H13 steel (500°C) for their different microstructures. After aged at 550°C for 50h, a much higher hardness (about 53 HRC) can be retained in the spray-formed H13 steel, showing an excellent thermal stability at 550°C.