Advanced Materials Research Vols. 97-101

Abstract: The scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were used to characterize samples prepared from the surface scum of melt, the middle flake residues on the furnace wall and the “bottom bulk” after the A357 alloy pouring. The morphology and impurities composition of these features were investigated. Some of particles and regions in samples during the analyses were also studied in detail. The results of analyses show that the surface scum of melt include Al2O3, MgO or MgAl2O4; the impurities of the middle flake residues is comprised of Al2O3, MgO or MgAl2O4, as well as SiO2 particle, Al9Fe2Si2 compound and dimple like C-rich areas; the bottom bulk contains C-rich impurities such as Al4C3 or some of unknown phase or elemental carbon.

Abstract: The structure and properties of A357 aluminum alloy with different second dendrite arm spacing (SDAS) in different situations of overheating were investigated. The results indicate that serious overheating characteristic structure takes on compound melting ball, crystal separating phase and overheating triangle section; The overheating level of A357 alloy raises with solution temperature increasing; The mechanical properties decrease with the overheating level increasing; The overheating temperature of casting increases as the SDAS decreases, the regression equations of the correlation between SDAS and overheating temperature is as follows: T = 575.46-0.213SDAS; Optimum solution temperature could be selected for A357 alloy with different SDAS depending on supercritical solution region proposed in this paper.

Abstract: A vertical type tandem twin roll caster which can cast clad strip was devised and assembled. The casting of the clad strip was tried. The three layers clad strip could be cast by a vertical type tandem twin roll caster at only one process. The clad strip was connected directly from AA8079 and AA6022 at roll speed of 30m/min. The diffusion area between the strips was very narrow. The interface between the strips was clear and flat. The strips were bonded firmly.

Abstract: Roll casting of Al-25mass%Si hyper eutectic aluminum alloy strip was tried by an unequal diameter twin roll caster. The casting speed was 10m/min. The thickness of the strip was about 2mm. The eutectic Si and primary crystallized Si were very fine by the effect of the rapid solidification. The size of the primary crystallized Si was not uniform at the thickness direction. The primary crystallized Si at the near surface was finer than that of inside. The eutectic Si was finer than 2μm. The strip could be cold rolled after hot rolling and annealing.

Abstract: The numerical simulation and application experiment are used to research the electromagnetic stirring (EMS) in Angang steel company limited. The results show that the stirring effect in side to side position of EMS rolls is better than that in face to face position. And the stirring effect in triples zero patterns are better than that in the double butterfly patterns. The application effect of EMS in Ansteel is obvious. The equiaxed zone in different steel grade such as low carbon aluminum killed steel, pipe steel, silicon steel and high carbon steel is improved 12-25% with EMS. And the slab center segregation has an obvious decreased after using EMS.

Abstract: Mechanical properties of heat treated 30CrMo steel produced by CSP (Compact Strip Production) and conventional continuous casting process. Results showed that 30CrMo steel produced by CSP exhibits higher hardness than that produced by conventional continuous casting process. The higher hardness was attributed to fine-grained microstructures in the as-rolled CSP strips.

Abstract: Heterogeneous nucleation is a critical factor for grain refinement magnesium alloys. The paper reports the Al-9wt.%Mg-10wt.%SiCp master alloy were prepared by adding SiCp into the Al-Mg molten with stirring in 610-595°C, which were introduced into AZ91. Experimental results indicated Al4C3 were in situ synthesis on the surface of SiCp by the reaction between SiCp and Al in 850°C, which could be as nucleant substrate for primary Mg during the solildification of magnesium alloys. This investigation provided a novel idea for grain refinement Mg-Al alloy.

Abstract: Al-10.5Zn-2.0Mg-1.5Cu alloy was produced by spray forming (SF) technique. The initial microstructure, particularly secondary phases, present in the as-SFed alloy was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with attached energy dispersive X-ray spectroscopy (EDS). The results indicated that the equiaxed α-Al grains have an average size of about 18-20 μm in diameter. The intergranular phase was identified as MgZn2 by selected area electron diffraction (SAED) pattern, which was also distributed in the grain interior as well as Al2Mg3Zn3. A needle-like Al23Cu(FeCrMn)4 precipitate was detected. The combined analysis of morphology and crystallographic structure suggested that the Al23Cu(FeCrMn)4 grew along its long axis of <001> orientation. The refinement of the intergranular phases occurred, which is probably due to a decreased amount of eutectic liquid phase finally solidifying on a large area of grain boundaries.

Abstract: This paper describes the twin-roll casting technology of magnesium alloys that contain relatively high weight ratios of aluminum, such as AM60, AZ91 and AZ121. The magnesium alloy sheets were cast by a vertical roll caster to manufacture relatively high-strength Mg alloys with high aluminum content. The influences of such process parameters as roll materials, casting temperature, and roll speed were ascertained. A simple method of predicting the convection heat transfer coefficient between casting rolls and molten metal is introduced. The microstructures of cast magnesium alloy sheets are microscopically observed to investigate the effects of roll-casting conditions on crystal growth in the cast products. It was found that Mg alloys with high aluminum content can be fabricated at a roll speed of 90m/min with a vertical-roll caster. The grain size of the manufactured wrought magnesium alloy sheet was about 30 micrometers due to rapid solidification in the proposed process.

Abstract: One internal friction peak associated with the B2↔B19’ transformation appears on the cooling curve of porous NiTi shape memory alloy and the dense NiTi alloy shows the maximum peak. The tan δ value increased with the increasing of strain amplitude and the decreasing of frequency. Tan δ value of porous alloy mainly comes from the energy absorbing of the matrix at the small strain amplitude, however, if the strain amplitude is large, the tan δ value comes from the energy consumption that overcomes the friction between folds and the plastic contribution.