Papers by Keyword: Si Content

Abstract: In a vertical type high-speed twin-roll caster, the adhesion of solidified aluminum alloy to the nozzle (ASAN) makes problems with the quality of the strip surface. The effects of the Si content of Al–Si alloys and the casting conditions on the ASAN were investigated. Alloys with Si contents of 0%, 0.5%, 1%, 2%, 3%, 6% and 10% were considered. The ASAN was high for Si contents of 0.5%, 1%, and 2%. This demonstrates that there is a relationship between the quasi-solid state and the ASAN. As the roll speed and molten metal temperature increased and solidification length decreased, the ASAN decreased. On the basis of these results, the stagnation of molten metal near the nozzle plate was investigated. A gap of 5 mm was introduced between the nozzle plate and the roll surface to eliminate the stagnation of molten metal, resulting in reduction of the ASAN.

Abstract: In this study, we investigated the effect of Si and Mo on the sigma-phase precipitation in S32750 super duplex stainless steel slab. The activity for Mo with increasing Si and Mo was calculated by the Wagner formula, and the equilibrium solidification phase diagrams of S32750 duplex stainless steels with different Si and Mo contents were calculated using the thermo-calc software. The sigma phase precipitated mainly at ferrite/austenite phase boundaries and grew up towards the interior of ferrite phase in S32750 SDSS slab. The area fraction and size of the sigma phases significantly increased with increasing Mo content and Si content. Also, the increment in Mo and Si content affected the Mo concentration in sigma phase. The sample（Mo:3.4%,Si：0.3%） had a lowest sigma-phase area fraction of 2.84% and had lowest Mo content in σ phase.The calculation results showed that the increase of Mo and Si content increased the initial precipitation temperature and maximum precipitation amount of σ phase in S32750 SDSS equilibrium phase diagram. The activity of Mo also increased with increasing Si content and Mo content. That is, Mo and Si elements promoted the precipitation of σ phase.

Abstract: Si ranging from 0.2 mass% to 2.0 mass% was added to Al-5%Mg alloy (5182) and strip was cast by a vertical type high-speed twin-roll caster at a speed of 80 m/min. The as-cast strip was cold-rolled down to 1 mm thickness and annealed. The mechanical properties were investigated using cup tests and tension tests. The limiting draw ratio (LDR) of the 5182 alloy was 2.0 and the LDR became smaller as the Si content increased. When the Si content was 2.0 mass%, the LDR was 1.8, which shows that Si-added 5182 can be used for sheet forming, if the Si content is less than 2.0 mass%. The tensile strength and elongation were almost constant when the Si content was less than 1 mass%, but decreased at 2.0 mass% Si. However, the elongation was greater than 20% at 2.0 mass% Si. For die casting, 2.0 mass% Si was determined as the appropriate content from the results of the tension tests. When the Si content is in the range from 1.0 mass% to 2.0 mass%, then the Si added Al-5%Mg has the ability to be used for both die casting and sheet forming.

Abstract: The effect of annealing temperatures on surface morphologies, microstructure, and mechanical behaviors of CrAlSiN coatings with different Si content was investigated. EDX, XRD and SEM were employed to reveal the compositions and microstructure of CrAlSiN coatings. For Si content ≤8.6%, grain sizes reduced with temperature increasing to 400°C and then increased with further increase in temperature. For Si content ≥10.7%, grain sizes gradually reduced with annealing temperature increasing. When the annealing temperature arrived at 400°C, the hardness of CrAlSiN coatings with different Si content was much higher than as deposited. While the annealing further increased to 800°C, the hardness of CrAlSiN coatings with Si content ≤8.6% reduced, but the hardness of CrAlSiN coatings with Si content ≥10.7% continued to increase.

Abstract: The shear behavior of aluminum alloys containing increased amounts of Si or Mg compared with the 6061 alloy has been investigated by carrying out isothermal and non-isothermal tests in the mushy state during solidification. In isothermal conditions, it is shown that (i) an increase in Mg content leads to a more resistant semi-solid alloy compared with the 6061 alloy for the same solid fraction and (ii) an increase in Si content leads to a more brittle mushy alloy. In non-isothermal conditions, stress increases continuously with decreasing temperature with the formation of cracks for some compositions. This study shows that an increase in Mg content seems to be the most appropriate solution to reduce the formation of cracks in a solidifying 6061 alloy.

Abstract: The effect of Si content on structure and wear resistance of cold roll steel with 5%Cr by using vacuum arc melting furnace had been studied in this paper. Results showed that with increasing Si content martensite got coarsening and the number and content of primary carbide increased; The type of primary carbide was M7C3 and Si mainly dissolved into martensite by XRD analysis; The wear resistance was effectively improved while Si content increased. The appropriate Si content in cold roll steel with 5%Cr was 1.5%~2％.

Abstract: Effects of silicon concentrations in Ni-Cr-based alloys on the formation of oxide scales were examined in reduced atmosphere. The morphology and oxide scale were compared based on the Si content. The formation and growth kinetics of the oxide scale are rather sensitive to the alloy microstructures and their corresponding Si contents. Oxide ridges formed on the eutectic structure preferentially, while a thinner and homogeneous oxide scale grew from the austenite matrix. The thicknesses of the oxide ridges and the oxide layer on the austenite matrix are dependent of their corresponding Si contents. The ridge-like feature indicates that the austenite/carbide phase boundaries offer fast diffusion paths for metal atom outward diffusion. The formation of SiO2 sub-layer at the oxide scale/metal interface can act as an effective diffusion barrier for atom outward diffusion.

Abstract: Three layer clad brazing sheets composed of Al-7.5Si alloy (filler, thickness:10 ㎛ )/Al-1.2Mn-2Zn-(0.04-1.05)Si alloy (core, thickness:80 ㎛)/Al-7.5Si alloy (filler, thickness:10 ㎛), were produced by laboratory fabrication, through casting, hot rolling, cold rolling, intermediate annealing, and final cold rolling. The effects of Si content in the core(0.04-1.05wt.%) and reduction rate of the final cold rolling(10-45%) on microstructure and brazing behavior were investigated. The results revealed that the microstructure and brazeability of the brazing sheet are governed both by Si content in the core and by the reduction rate of the final cold rolling. The excellent brazeability was obtained when the core alloy has the Si content of/cold rolled to 0.04%/10-45%, 0.41%/20-45% and 0.64%/30-45%. In these cases, a coarse grain structure was developed in the core during the brazing process, which suppressed the penetration of melting filler into the core.

Abstract: Effect of silicon content on the creep properties of Ti-6Al-4Fe-xSi was studied. Creep resistance of Ti-6Al-4Fe-xSi alloys was superior to that of Ti-6Al-4V. Ti-6Al-4Fe-0.5Si alloy exhibited the highest rupture strength and creep resistance among the Ti-6Al-4Fe-xSi alloys investigated. The minimum creep rate of the alloys decreased with increasing silicon content up to 0.5wt.% and then it increased again when the silicon content was higher than 0.5wt.%. TiFe precipitates were formed mainly at the β phase area of Ti-6Al-4Fe-xSi alloys by consuming titanium and iron in β phase, when the alloys were thermally exposed at 500 and 600°C during the creep test. During the creep test, microvoids were induced at the TiFe/α phase interfaces and the cracks were formed along the TiFe/α phase interfaces by the coalescence of the voids. Those cracks were finally connected each other through the α phase.