Papers by Keyword: Extrusion

Abstract: This paper presents our experimentation and modeling efforts to study the pattern of material flow in the extrusion and deposition stages of the Contour Crafting (CC) process. Specifically, we performed a preliminary finite element analysis (FEA) of extrusion and deposition mechanisms with clay as the fabrication material. Using the FEA simulations, we derived certain basic understandings of the effect of extrusion orifice geometry on the performance of CC. We found that a square orifice is most aptly suited, both in terms of delivering the optimal fusion between layers as well as creating the desired external surface profile. Our experiments validate these results.

Abstract: The superconductive MgB2/Al composite material with low and high volume fractions of particles were fabricated by our special 3-dimensional penetration casting (3DPC) method. The composite material showed homogeneous distribution of MgB2 particles in the Al-matrix with neither any aggregation of particles nor defects such as cracks or cavities. The critical temperature of superconducting transition (TC) was obtained via electrical resistivity and magnetization to be about 37 ~ 39K. The Meissner effect was also verified in the liquid He, in which a piece of the composite floated above a permanent magnet. Extruded rod and wire were successfully fabricated and they also showed onset TC of 39 K on their electrical resistivities as the same as the billet sample.

Abstract: The as-cast microstructure of Mg-5Al-3Ca-2Sm alloy consists of equiaxed α-Mg matrix, (Mg, Al)2Ca eutectic phase and Al-Sm rich intermetallic compounds. This eutectic phase of the extruded alloys was elongated to extrusion direction and size of this phase was finered compare to that of as-cast alloys because of severe deformation during hot extrusion. After hot extrusion, the average grain size of Mg-5Al-3Ca and Mg-5Al-3Ca-2Sm alloys was 4.8 *m and 3.8 *m, respectively. In load-unload hardness test, penetration depth was decreased with added Sm and after extrusion procedure because of grain size refining by addition Sm and large deformation. Hardness value of the alloys containing Sm was higher than that of Mg-5Al-3Ca alloy due to grain refining and formation Al-Sm rich intermetallic compound at gain boundary and α-Mg matrix. Maximum hardness value was obtained at the extruded Mg-5Al-3Ca-2Sm alloy at elevated temperatures.

Abstract: The presence of surface defects, such as streaking, is one of the most serious quality issues for 6000-series aluminium extrusions. The formation of a streaking defect near a web intersection of a hollow profile was investigated in detail. The streak was apparent on the extrusion in both the as-extruded and the as-anodised conditions. Microstructural examinations indicate that the streaked region contains different surface imperfections compared to the normal region and smaller grains and stronger texture than the normal region. The effects of die design and microstructural variables on the formation of streaks on aluminium extrusions are discussed.

Abstract: For development of high strength magnesium alloys, a melt stirring method was employed to Mg-Al and Mg-RE (rare earth metal) alloys. As reinforcement particle, B2O3 powder was added into melts and stirred at 953K in 10 or 20 minutes with argon atmosphere. The grain sizes of both alloys were decreased by 3wt% B2O3 addition. These results show that B2O3 have grain refinement effects to magnesium alloys. Micro Vickers hardness of Mg-Al alloy was increased by 3wt% B2O3 addition. On the other hand, the hardness of Mg-RE alloy was decreased by B2O3. Though addition of B2O3 into Mg-Al and Mg-RE systems make grain size to fine, the hardness of Mg-RE alloys decreased. The tensile properties of Mg-RE alloys with B2O3 were extremely improved by extrusion process.

Abstract: The wrought magnesium alloys AZ80 and ZK60 were extruded at 175°C ≤ T ≤ 350°C at an extrusion ratio of ER = 12. With decreasing extrusion temperatures a marked refinement in grain size was found for both alloys resulting in higher values of yield stress while UTS values were hardly affected. As opposed to AZ80, a marked yield stress differential between loading in tension and compression was observed in ZK60, this effect being explained by the differences in crystallographic texture.

Abstract: Microstructures developed by warm extrusion for Mg97Zn1Y2 alloy including long-period stacking order (LPSO) phase have been investigated using SEM and TEM. The extruded magnesium alloy with LPSO phase exhibits high strength and sufficient ductility. Such superior mechanical properties appear by warm extrusion around the temperature of 623K. The microstructure of the extruded alloy consists of matrix of fine-grained hcp phase and elongated grains with fine-lamellae including LPSO phase. The grain size of hcp matrix was about 1μm, indicating that remarkable grain refinement was occurred by extrusion since the grain size of as-cast alloy was about 500μm. Special attention has been paid on the enrichment of solutes at stacking faults and grain boundaries in the fine-grained matrix, which would contribute not only to the strengthening but also to the stability of fine-grained structure because of its role of an inhibiter against grain coarsening.

Abstract: While magnesium cast components have found their application in the transportation industries the interest is now spreading to wrought alloys due to the possibility to get even more homogeneous and better properties compared to cast parts. Therefore alloy and process development especially for extrusion is a main concern to enhance the application of Magnesium wrought alloys. This paper gives an overview on the actual status of the process and alloy development of extruded Magnesium wrought alloys.

Abstract: Die wear is regarded as a crucial factor which affects die life and quality of products. In hot extrusion process, finite-element method (FEM), BP neural network and genetic algorithm were combined together to optimize extrusion die profile which yielded more uniform wear depth distribution on die profile. A method of B-spline function interpolation was used to describe extrusion die profile. The temperature, pressure and velocity field of nodes that lied on extrusion die profile were gained by FEM simulation. Wear depth of extrusion die profile was calculated by modified Archard theory. The results were used to train BP neural network, so that nonlinear mapping relations between reference points of die profile and wear depth were obtained. In order to gain uniform wear depth, genetic algorithm was applied to optimize extrusion die profile. Optimum result, compared with common conical die profile, reduced wear depth of extrusion die and improved service life. At the same time, the optimal result accorded with practical conditions.

Abstract: The fracture mechanisms of SiCp/AZ91 composites were investigated by scanning electron microscopy (SEM). For the as-cast composites, the decohesion at SiCp/matrix interface is the main fracture mechanism because of the high stress concentration resulting from the segregation of particles in grain boundaries formed during solidification process. But for the extruded composites, the main fracture mechanism is the particle crack or ductile rupture of the matrix between the particles. So the fracture mechanism of SiCp/AZ91 composites is altered by extrusion because the segregation of particles and defects in the grain boundaries are largely eliminated by extrusion.