You Junhua

Effects of Ca on Microstructure and Mechanical Properties of ZA62 Alloys

Effects of Ca element on microstructure and mechanical properties of ZA62 alloys were investigated by using zeiss microscope, scanning electron microscope equipped with an energy dispersive spectrometer, X-ray diffractometer, and electronic universal testing machine. The results show that Ca can significantly refine microstructure and cause the precipitation of Mg2Ca and Al2Ca phases on grain boundary of ZA62 alloys. The addition of Ca can improve the tensile properties of alloys at room temperature. When the content of Ca is 2%, good properties are obtained, the tensile strength and yield strength of Mg-6Zn-2Al-2Ca alloy reaches 240.79MPa and 82.78MPa respectively.

Characteristics of array holes with large aspect ratio in aluminum-based cast alloy

ABSTRACT Array holes were obtained by machining methods or nontraditional machining methods, and casting process was rarely used in the preparation of array holes. In this experiment, stainless steel thin rods coated with alcohol group graphite paint were chosen as cores to prepare array holes on aluminum-based cast alloys, and the roughness and roundness of holes were analyzed. The results show that array holes cast with 2 mm pitch of holes, 0.54 mm diameters, and large aspect ratio of 100 were obtained. The roundness and roughness of holes were influenced by consumption of carbon element from surface of hole core and wettability between molten metal and hole core surface; the lower roughness and the better roundness could be acquired under these experimental conditions. And roughness of holes (Ra) was about 6.3 µm, which is close to that obtained by machining, and the value of hole shape factor (K, characterizing the roundness of the hole) was above 0.7; the shape of the hole approached a circular shape.

Study on the Hot Tearing Susceptibility of Mg‐7Al‐xCa‐2Si‐0.8Zn‐0.5Sr‐0.4Mn Heat‐resistant Magnesium Alloys

The Mg-7Al-xCa-2Si-0.8Zn-0.5Sr-0.4Mn(x=1,2,3,4wt%) alloys cylindrical specimens were fabricated using the same length metal mold. The hot tearing susceptibility of alloy is evaluated by the Crack-rod critical diameter and hot tearing sensitive coefficient. The optical microscopy, scanning electron microscopy (SEM) and the detector of energy dispersive (EDX) were used to investigate the hot tearing behavior of magnesium alloys. The results indicate that the microstructures of alloys are refined with Ca addition When the Ca content is 3.0%, the crack-rod critical diameter and hot tearing sensitive coefficient are both the lowest, at the same time, the fracture area of α-Mg dendrite is zero and that of eutectic phase is 100%. In the crack formation process, the eutectic phase have the trend of enrichment to crack and the ability to fill in cracks, so the hot tearing susceptibility of alloy is reduced.

Effect of Si and Ca Additions on Microstructure of As-Cast Mg-Sn-Sr Alloy

Alloying elements Si and Ca were employed to the Mg-5Sn-0.5Sr alloy in order to improve the heat resistance properties of Mg alloys. Mg-5Sn-0.5Sr-xSi (x=1, 2) and Mg-5Sn-0.5Sr-ySi-0.5Ca (y=1, 2) alloys were fabricated using the pot resistance furnace under protection of N2+SF6 atmosphere. The phase constituent and microstructure of the as-cast alloys were analyzed by x-ray diffractometer (XRD), optical microscopy (OM) and scanning electron microscopy (SEM) respectively. The results show that the Mg2Sn phase, Mg2Si phase precipitate on the grain boundary during eutectic reactions and MgSnSr phase inside the grains as primary phase for as-cast Mg-5Sn-0.5Sr-xSi (x=1, 2) alloys, the volume fractions of Mg2Si phase increases with the increasing of Si element. For Mg-5Sn-0.5Sr-ySi-0.5Ca (y=1, 2) alloys, furthermore, the addition of Ca element can promote significantly the formation of primary (Ca, Sr)MgSn phases, inhibit the precipitation of Mg2Sn phase on the grain boundary. Both Ca and Sr additions can refine the Mg2Si phase.

Effects of Si on microstructure and mechanical properties of Mg-5Sn-2Sr alloy

Phase constitution and microstructure of the Mg-5Sn-xSi-2Sr (x=0, 1, 2) alloys were analyzed by X-ray diffractometer, optical microscope and scanning electron microscope with an energy dispersive spectrometer. The tensile properties of the alloys were tested by electronic universal testing machine, and the fracture surfaces of the alloys were observed with scanning electron microscope. The results show that the microstructure of the Mg-5Sn-2Sr alloy consists of α-Mg, MgSnSr and Mg2Sn phases. The addition of Si element can promote the formation of Mg2Si phase on the grain boundary, and the content of Mg2Si phase increases with increasing the Si element. Mg2Si is a strengthening phase, which can effectively prevent grain boundary sliding and dislocation motion, and thus, the mechanical properties of the alloys were obviously enhanced. The mechanical properties of Mg-5Sn-2Si-2Sr alloy are better than other alloys, the tensile strength, yield strength, elongation and hardness are 147MPa, 110MPa, 5.0% and 47HB respectively.

Fabrication of High Performance Fe-Si-Al Soft Magnetic Composites

Soft magnetic composites (SMC) offers several advantages over traditional soft magnetic materials, for example, new shaping possibilities opens up for 3D design, very low eddy current loss, high magnetic permeability, high resistivity and low coercivity[1]. In recent years, effect of particle size, magnetic particle content, compaction parameters and annealing parameters on properties of soft magnetic composites has been verfied[2-6], and some theoretical works have been studied[7,8]. The conventional Fe-Si-Al (sendust) alloys are known to have several advantages, which include magnetostriction of 0, anisotropy constant of 0, higher electrical resistance, high permeability and lower cost[9,10]. The soft magnetic composites fabricated with Fe-Si-Al powder have a higher performance-cost and have a quick rising output all over the world. But few published information can be found about Fe-Si-Al soft magnetic composites.In this study, the effect of shaping pressure, annealing tempreture, magnetic annealing and dielectric content on properties of Fe-Si-Al soft magnetic powder cores was investigated. Through experimental optimization, the optimum process parameters were obtained.