Advanced Materials Research Vols. 1004-1005

Abstract: Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to study the microstructure and mechanical behavior of an Al-Cu-Mg alloy after tensile test at 125°C, 150°C, 175°C and 200 °C, respectively. The yield strength and ultimate tensile strength decreased with the increase of temperature, while the elongation increased firstly and then decreased. The S and S′ precipitate after tension at elevated temperatures. When the temperature was higher than 175°C, the precipitate coarsens rapidly. The alloys displayed a shear fracture features at elevated temperature. The larger S′ and S phase coarsened and dropped which forming crack in the grain boundaries and precipitate interfaces, resulting in the decrease of the elongation of the alloy.

Abstract: The surface of AZ31 magnesium substrate is coated by Zn-Al alloys using cast-penetrated cladding. The transverse section of alloy cladding is composed of cladding zone, diffusional zone, and bonding zone. The microstructure evolution, phase constitution, and chemical composition of the transition layer are studied. The experimental results exhibit cladding zone contained dendrite matrix and interdendritic eutectic structures. The plume eutectic structure and columnar eutectic structure are formed in diffusional zone and bonding zone, respectively. Zn and Al solid solutions gradually decrease and disappear owing to the diffusion of magnesium atom and the changes of magnesium element concentration. Mg₇Zn₃ phases are generated rapidly due to the interdiffusion of zinc and magnesium atoms rapidly in the diffusional zone and bonding zone. As Mg-Zn eutectic phases hinder the movement of Mg and Al atoms, the Mg-Al intermetallic compounds are eliminated completely. The microstructure is transformed into Mg solid solution and Mg₇Zn₃ eutectic structure to combine with AZ31 base metal.

Abstract: Microstructures of metal micro parts after microforming at elevated temperatures must be evaluated due to mechanical properties depend on average grain size. In this work, the effects of specimen diameter on the microstructure and microhardness of a hot-extruded AZ31B magnesium alloy were studied. Obvious size effect on microstructure and microhardness of the alloy could be observed. The size effects could be explained by strain distribution and dislocation density differences between the two kinds of specimens.

Abstract: Based on first-principles calculation, the mechanism of optimal pre-deformation temperature (Ms+30) for NiTiNb alloy was characterized and analyzed by several parameters, such as crystal constant, cohesive energy and the elastic constants. Simulation results showed that the shear modulus c′ and c₄₄ of matrix NiTi phase was softened at 208K. At the same time, its cohesive energy obtained its local maximum value, which was originated from the easy transition ability of valence electrons in d orbital. In other words, the matrix NiTi phase was instable only when the pre-deformed temperature was not only for Ms but also to 208K (Ms+30K).

Abstract: Mg/Al dissimilar materials were welded successfully by GTAW with SAlMg-1 and SAlMg-2 welding wire of Mg-Al system. The nice weld shape and free defects of joints are obtained. The test results indicated that continuous lamellar intermetallic compounds is not found The structure of Mg side in the fusion zone is composed of α-Mg solid solution+ β-Al₁₂Mg₁₇ eutectic structure and precipitates β-A1₁₂lMg₁₇ on the grain boundary. The structure in the weld zone is mainly α-Mg solid solution + β-A1₁₂lMg₁₇ solid solutions. Mg and Al content are stable in the fusion zone of Mg side. However, in the weld zone of Mg side the Mg content is decreased gradually, and the Al content is increased that reaches a stable level in the weld zone of Al side. As a result, when Mg content in the wire can hold a proper level, the intermetallic compounds will be controlled effectively, and the performance of AZ31/7005 welding joint can be improved.

Abstract: Industrial AM60 magnesium alloy, to which mixed rare earth containing Y, Gd and Nd elements is added, was used to study the effects of rare earth (RE) on their casting microstructures and properties. The experimental results showed that RE could effectively improve grain refinement and the internal organization, which transferred the Mg17Al12 phase from the network structure into grainy one. The microscopic analysis indicated that by adding the mixed RE, the amount of Mg17Al12 compounds was less than that without mixed RE on the grain boundaries, and it was replaced by Al-RE compounds. In addition, the mechanical properties of the alloy with mixed RE had been significantly improved and the maximum tensile strength was up to about 260MPa and the elongation rate could reach more than 10%. When the mixed RE content was more than 2%, coarse Al-RE compounds were formed in the alloy, which degraded the mechanical properties.

Abstract: A series of annealing parameters including the cooling rate and overaging time, especially ultra high cooling rate of a ultra-low carbon auto steel were conducted on HDPS (hot dipping process simulator) in experiment. The research results show that, when samples were conducted under extra fast cooling rate higher than 30 °C/s, yield and tensile strength almost changed not when cooling rate increased from 30 to 50 °C/s, as cooling rate reached 90 °C/s, the strength and elongation changed more rapidly. When the overaging time changed from 130 to 300 s, the elongation was more sensitive, changed from 19.7 to 25.6 %. Yield and tensile strength were not sensitive when aging time was below 213 s, but with increasing aging as high as 300 s, the yield strength decreased 11 MPa, and tensile strength decreased 21 MPa.

Abstract: Two types of DP steels which contain high carbon and high silicon respectively were produced on industrial production line. The microstructures and mechanical properties were investigated. Based on the thermodynamics and kinetic analyses, the intercritical austenization was researched. The results show that the high silicon and low carbon composition used to DP steel can avoid martensite band structure and decrease the martensite fraction, which will improve the elongation and work hardening ability. Phase transformation kinetic analysis indicates that high silicon content can make manganese enrich in austenite and stabilize austenite in intercritical region. Assisted by the strengthening role of silicon in austenite, the mechanical properties of high silicon and low carbon DP can fully meet the standard.

Abstract: A new cold rolled hot-dip galvanizing DP450 steel with low carbon and high chromium was designed and effect of the galvanizing processes on the microstructure and mechanical properties was also investigated. At last, it was compared with the referenced DP450 steel which was already produced in industry. The results show that microstructure of the experimental steel consists of regular polygonal ferrite, almost 1% MA island and little bainite. The industrial experimental cold-rolled galvanizing DP steel has excellent combined mechanical properties as follow: yield strength is 306 MPa, tensile strength is 467 MPa and elongation (A80) is 33%. Compared to the referenced steel, the experimental DP450 steel has lower yield strength, better elongation and better forming performance, accordingly.

Abstract: High purity AL₂O₃-MgO carbon-free refractories for ladle lining were investigated, this paper compared with the properties of bricks with different bond system and different production process, and study the wear mechanism, the TOC and hydrogen content change; analyzing the microstructure of residual bricks and the impact of refractories on quality of molten steel;Conclusions:The two kinds of bricks have different wear mechanism, the bricks bonded by a-bond was damaged mainly by penetration and erosion while the bricks bonded by resin was damaged by structure spalling and they have different effect on cleanness of molten steel.