Ren Guo Guan

Microstructure formation mechanism and properties of AZ61 alloy processed by melt treatment with vibrating cooling slope and semisolid rolling

A melt treatment with a vibrating cooling slope and a semisolid rolling process to produce an AZ61 alloy strip was proposed. The microstructure formation mechanism and the properties of the AZ61 alloy produced by the proposed process were investigated. Due to the high cooling rate and stirring action caused by the vibration cooling slope, the nucleation rate was greatly improved, which caused the formation of fine spherical or rosette primary grains. During the rolling process, the solid fraction increased from the entrance to the exit of the roll gap, and under the shearing action of the roller, the distribution of solute in the melt was homogenous, and the primary grains grew further. When the casting temperature was 680 °C, a strip with a cross section of 4 mm×160 mm was produced and a homogeneous microstructure was obtained. The ultimate tensile strength of the AZ61 alloy strip produced by the proposed method reached 242 MPa, and the corresponding elongation to failure was 4%, which were better than those achieved in previous similar studies.

New Magnesium Alloys for Potential Application of Implantation Biomaterial

New magnesium alloys with optimized chemical compositions with good biocompatibility were designed. Experimental results show that MZ alloy mainly consists of Ca2Mg5Zn5+α (Mg) and MgZn+MgZn2+Mg2Ca+Zn-Zr compounds. Ca has a strong capability for grain refinement in such alloy. Zr can refine magnesium alloy. Zn addition does not refine the solidification microstructure but plays significant strengthening role during aging treatment. The main strengthening phases of Mg-Zn-Zr alloy are γ(MgZn) and δ(Mg2Zn3). The tensile strength of MZ alloy plate aged at 170°C for 12h is 320MPa, and the elongation-to-failure is 18.4%, the alloy has a potential application of implantation biomaterial.

Microstructure formation mechanism and properties of a Mg-3Sn-1Mn (wt%) magnesium alloy processed by a novel semisolid continuous shearing and rolling process

A novel semisolid Continuous Shearing and Rolling (CSR) process for producing a Mg-3Sn-1Mn (wt%) alloy strip is developed, and the microstructure formation mechanism and properties of the Mg-3Sn-1Mn (wt%) alloy processed by this process are investigated. At a casting temperature of 690°C and a roll speed of 0.052 m·s−1, a Mg-3Sn-1Mn (wt%) alloy strip with a cross section size of 4×160 mm was produced by the proposed process. Under strong cooling and shearing actions, eruptive nucleation, direct globular grain growth and dendrite arm breakage took place during the process, which caused formations of fine spherical grains. The grain size and roundness of the Mg-3Sn-1Mn (wt%) alloy strip increased with increasing increments of the casting temperature. In this perspective, roll speed obviously affects grain shape. The ultimate tensile strength and elongation of the Mg-3Sn-1Mn (wt%) alloy strip reached 205.93 MPa and 7.2%.

Effect of Heat Treatment on the Microstructures and Mechanical Properties in AZ31 Magnesium Alloy Processed by Continuous Rheo-Extrusion

AZ31 magnesium alloy profiles were prepared by continuous rheo-extrusion process, and effects of solution and aging treatments on the microstructures and mechanical properties was investigated by OLYMPUS optical microscope, scanning electron microscope, energy dispersive spectroscopy device and tensile machine. The results reveal that saturated solid solution was formed in the profile at a solution temperature of 415 °C and 16 hours. During aging treatment of saturated solid solution, β-Mg17Al12 phase nucleates firstly at grain boundaries and takes on globular growth, which is mainly due to the lower interfacial energy in coherent or semi-coherent interface between β-Mg17Al12 phase and matrix phase. Lower interfacial energy is favorable to the nucleation and growth of β-Mg17Al12 phase at grain boundary. With the increase of aging time or the rise of aging temperature, β-Mg17Al12 phase precipitates out gradually from grain interior and starts to grow in globular shape. After β-Mg17Al12 phase grows to a certain extent, it grows in lamellar shape along the orientation of lower mismatch between β-Mg17Al12 phase and matrix phase. After solution at 415°C and 16h and aging at 180°C and 8h, the ultimate tensile strength and elongation to failure of the profile are 305MPa and 13%, respectively.

Microstructure and Mechanical Properties of Al-Mg-Sc Alloy Processed by Semi-Solid Continuous Casting-Extrusion

High tensile strength Al-3Mg-0.5Sc alloy wires can be produced by a method called semi-solid continuous casting-extrusion and on-line solution process (CCES). The effects of artificial aging and the combination of the artificial aging and cold drawing on the microstructures and properties of alloy wires were respectively investigated. TEM observations reveal that a large number of dislocations and Al3Sc particles distributed in the Al-matrix of Al-3Mg-0.5Sc alloy produced by semi-solid CCES.After directly artificial aging (DAA), the tensile strength is 353MPa and elongation is 19.9%; After cold drawing following artificial aging (CDAA), the tensile strength is 378MPa and elongation is 17.7%; After artificial aging following cold drawing (AACD), the tensile strength is 435MPa and elongation is 10.4%.

Microstructure Formation and Mechanical Properties in AZ31 Alloy Processed by Continuous Rheo-Extrusion

Based on continuous casting and extrusion (CAXTEX) process, a semisolid metal forming process, continuous rheo-extrusion of magnesium alloy, was proposed. Effect of casting temperature on semisolid region distribution, microstructure formation and stability of forming process, as well as microstructure and mechanical properties of the AZ31 alloy fabricated by the process were investigated. Microstructure evolution from dendrite to rosette or spherical grains was observed with the application of large shearing force provided by the roll. The results indicate that semisolid region in the roll-shoe gap moves downward gradually with the increase of casting temperature, and proper casting temperature range of 730~750°C is suggested. Under the suggested casting temperature, 10×15mm sectional bar of AZ31 alloy with smooth surface and homogeneous striped microstructure has been obtained. As the product was aged for 14h at 180°C after 16h solution at 415°C, the ultimate tensile strength and elongation could reach 305MPa and 11.5%, respectively.

A Novel Process for Grain Refining and Semisolid Processing

A novel process for grain refining and manufacture of high quality semisolid slurries ofalloys was developed. The process was proven to refine metal grain remarkably, and the grain sizeof pure aluminum can be refined to the first grade of Chinese refining standard of pure aluminumGB/T 7946.4-1999 ref) . P rimary silicon and eutectic silicon in the hypereutectic Al-Si alloy can bealso effectively refined. This process was used to prepare the billets with small spherical grains orequiaxed grains of Al-6Si-2Mg, AZ91, AZ31 and hypereutectic Al-Si alloys successfully. The p ip es ,profi le s and wire s of 6201, AZ31 and AZ61 alloys were produced by continuous rheo-extrusion.The strips of AZ91, AZ31, and Mg-Sn alloys were prepared by rheo-rolling. As an innovativeprocessing technology with low cost and high efficiency, vibrating sloping plate melt treatment hasgood prospective application in many fields such as rheo-casting, rheo-extrusion, rheo-rolling,metal microstructure refinement, etc.

Characterization of Magnesium Alloy Degradation in Whole Blood and Platelet Rich Plasma

Magnesium (Mg) is an attractive biomaterial due to its desirable biodegradable and mechanical properties. In this study, we compared the degradation behavior of Mg and a new Mg alloy incubated in both whole blood and platelet rich plasma (PRP) for two hours under standard cell culture conditions. To avoid settling of red blood cells, tubes with whole blood were under constant rotation during the incubation. Post-incubation solutions were collected, centrifuged, and analyzed for pH and Mg ion concentration. Mg and Mg alloy samples were fixed with a 3% glutaraldehyde solution, dehydrated using an ethanol series, critical point dried, sputter coated, and imaged with a field emission scanning electron microscope. Analysis of the post-incubation solutions showed PRP had greater concentrations of Mg ions and higher pH values when compared with whole blood. This indicated that the Mg and Mg alloy degraded faster when incubated in PRP than in whole blood. When comparing the surface of the materials after incubation with whole blood and PRP, the surfaces of Mg and Mg alloy that was incubated in PRP had larger cracks and grain boundaries than the samples incubated in whole blood. Additionally, more particulate microstructures were observed on the samples incubated in PRP as opposed to whole blood. Further studies are still needed to elucidate the differences in degradation of Mg alloys in whole blood and PRP.

Boundary layer and cooling rate and microstructure formation on the cooling sloping plate

During melt treatment by cooling sloping plate, laminar flow and turbulent flow exist on sloping plate surface commonly. The thickness of velocity boundary layer and the critical transfer distance from laminar flow to turbulent flow increase with the decrease of initial flow velocity. The thickness of temperature boundary layer increases with the increment of flow distance and the decrease of initial flow velocity. The melt cooling rate and melt thickness have an inverse proportion relationship. The melt cooling rate of cooling sloping plate process can reach 102–103 K/s and belongs to meta-rapid solidification scope. Uniform solute field and high cooling rate can lead to eruptive nucleation. In addition, a large quantity of heterogonous nuclei appears on the sloping plate surface, and vibrating flow can enable heterogonous nucleus to escape off the plate, which leads to nucleus multiplication. Under relative uniform solute field and high cooling rate, some grains can keep stable growth surface, go on growing with the round surface and finally maintain their globular structure. However, there are always some grains that grow along a certain preferred direction, but under vibrating flow their dendritic arms break and transform into near spherical structure.

The Impacts of Heat Treatment on the Material Structure and Properties of Mg-4.0Zn-1.0Ca-0.6Zr Bio-Medical Materials

The Mg-4.0Zn-1.0Ca-0.6Zr alloy was prepared through casting-homogenizing-rolling and the study was made on the alloy microstructure as well as mechanical properties under different heat treatment processes. The result shows that, alloy sheets have their hardness and tensile strength rising at the first phase and inclining later with the extension of aging time, in which the maximum values gained at 12h i.e. 71.2HV and 320MPa accordingly. At 8h of aging the extensibility obtained maximum value of 19.2%, then the value reduced gradually with the continuous aging time. The mechanical properties of alloy sheets increased after tempering process, the reason should be that, inside of the crystal particles rich amount of Mg6Ca2Zn3 and MgZn strengthening phases were separated out.