Magnesium Alloy Profiles Research Articles

Microstructure and mechanical properties of curved AZ31 magnesium alloy profiles produced by differential velocity sideways extrusion

Microstructure and mechanical properties of curved AZ31 magnesium alloy profiles produced by differential velocity sideways extrusion

Experimental and numerical investigation into rectangular tube extrusion of high-strength magnesium alloy

In order to reduce weight in air and ground vehicles, hollow magnesium alloy profiles are widely concerned. This research was aimed to extrude the tubes of newly developed high-strength alloy Mg–Al–Zn-RE by the porthole die. The magnesium alloy tubes with rectangular sections were extruded at the conditions optimized through the finite element simulations of extrusion processes. The microstructure observation indicated that the magnesium alloy underwent complete dynamic recrystallization (DRX) during the hot extrusion. Moreover, plenty of fine particles dynamically precipitated from the magnesium matrix were distributed on the grain boundaries. Undergoing the dramatical evolution of microstructure, the fine grains and particles significantly strengthened the extruded magnesium alloy. The tensile test demonstrated that extruded tubes possessed maximum ultimate tensile strength 406 ± 7 MPa and elongation 21.8 ± 1.0% at the optimal extrusion parameters.

Microstructure, mechanical properties and welding quality evaluation of longitudinal welds in hollow magnesium alloy profiles extruded at different ram speeds

Thin-walled and hollow profiles of magnesium alloys have more light-weight advantages. However, longitudinal welds exist inevitably in hollow profiles produced by porthole die extrusion. The welding qualities of the welds have a critical impact on mechanical properties of the profiles. In this paper, hot extrusion experiments of an asymmetrical hollow magnesium alloy profile extruded at different ram speeds were carried out. The effects of extrusion speed on grain structure, second phase particles, texture and mechanical properties of longitudinal welds in hollow profiles were systematically studied. The effects of microstructure and texture on mechanical properties of longitudinal welds were revealed. The fracture morphology and fracture mode of the welds extruded at different ram speeds were analyzed. A method based on K criterion for evaluating the welding quality of magnesium alloy profile in three-dimensional space was proposed. The values of three-dimensional welding quality factor K3D and non-dimensional welding quality factor K⁎ of the hollow magnesium alloy profile were determined respectively. Finally, the welding qualities of longitudinal welds in the hollow magnesium alloy profiles extruded at different ram speeds were evaluated.

Microstructure, Texture and Mechanical Properties of Extruded Mg-Zn-Zr Mg Alloy Profiles

Abstract The microstructures, texture and mechanical properties of large scale ZK60 magnesium alloy profiles were systematically investigated by XRD diffraction, microstructure observation and tensile testing at room temperature. The results indicate that there are mainly two phases in the extruded ZK60 Mg alloy, i.e. α-Mg and MgZn 2 , while a small amount of Mg 2 Zn 11 and Zn 2 Zr 3 phases were also observed. Initial coarse grains were significantly refined and broken down along the extrusion direction (ED), and partially dynamic recrystallization (DRX) also takes place during the hot extrusion process. The basal plane in most grains is aligned to ED and transverse direction (TD) rather than commonly extruded fiber texture. In the tensile test, the samples of 45ED direction exhibit the highest elongation to failure (δ=28% and 23%), and the ED direction reveal the highest ultimate tensile strength (σ b =325 MPa and 312 MPa) along middle and side parts, respectively.

Effect of Impulse Voltage on Microstructure and Corrosion Resistance of Microarc Oxidation Coatings on AZ80 Magnesium Alloy

Microarc oxidation coating and microarc oxidation-fluorocarbon coating were prepared on the surface of AZ80 magnesium alloy profiles. The phase structure, surface morphology and corrosion resistance of the coatings were investigated using SEM, XRD, copper sulfate spot test and polarization curve test. The main phase compositions of the microarc oxidation coatings were MgO, Mg2SiO4, MgSiO3, MgF2 and MgAl2O4. With increasing pulse voltage, the oxidation coating became thicker and the microstructure of the coating surface became compact; therefore the coating corrosion resistance was improved. The oxidation coating with pulse voltage of microarc oxidation controlled between 300-438V obtained the best corrosion resistance. The corrosion current density of magnesium alloy reduced 1-3 orders of magnitude after microarc oxidation treatment with increasing pulse voltage, and the corrosion resistance of microarc oxidation-fluorocarbon coating is desirable.

Effect of Hot Extrusion Process on Microstructure and Properties of Wide and Hollow AZ31 Magnesium Alloy Profiles

According to the profile section of transport equipment, the wide and hollow AZ31 magnesium alloy profiles was self-designed. Extrusion molding performance of the profiles, the law of microstructure and mechanical properties were studied when billets pretreatment and extrusion temperature were changed. The conclusions are as follows: (1) The grains of AZ31 profiles extruded by pre-extrusion billet are smaller and the strength is better, its maximum tensile strength is 280MPa. (2) Other processes being equal, the grains of AZ31 profiles are smaller and strength is higher, but the plastic is bad, when the extrusion temperature is 300°C. However, both strength and ductility of AZ31 profiles are better, when the extrusion temperature is 350°C. (3) Wide and Hollow AZ31 profiles perform significant heterogeneity and anisotropic characteristics on mechanical properties.

Microstructure and Corrosion Resistance of Microarc Oxidation Coatings on AZ31 Magnesium Alloy Extrusion Profiles

Microarc oxidation coatings were prepared on the surface of AZ31 magnesium alloy profiles. Oxidation time of the coatings was between 5min-10min. The phase structure, surface morphology and corrosion resistance of the coatings were investigated using SEM, XRD, copper sulfate spot test and polarization curve test. The results indicate: the main phase compositions of the microarc oxidation coatings are MgO, Mg2SiO4 and MgSiO3; with increasing pulse voltage, the micropore diameter of the coating surface becomes larger, the micropore number reduces and the coating surface roughness increases; the corrosion current density of magnesium alloy reduces significantly after microarc oxidation treatment. The pulse voltage of microarc oxidation should be controlled between 240V-360V to obtain the best corrosion resistance.

Effects of Annealing Parameters on Recrystallization of AZ31 Magnesium Alloy Processed by Continuous Rheo-Extrusion

AZ31 magnesium alloy profiles were prepared by continuous rheo-extrusion, and effects of annealing temperature and time on recrystallization of AZ31 magnesium alloy were investigated. The results reveal that when the profile is annealed in the temperature range from 200°C to 300°C, the moving velocity of grain interface with different dislocation densities on both sides increases with increasing annealing temperature, which is favorable to the formation of crystallized nucleus in the region in which interface sweeps over. As a result, the time required by the accomplishment of recrystallization becomes short. After recrystallization finishes, continuous temperature rise or prolonged holding time result in grain growth. When the profile is annealed at elevated temperature, with the prolongation of holding time, the grain growth rate accelerates obviously, and hence recrystallized microstructure becomes coarse. When the profile is annealed at lower temperature, the grain growth rate becomes small, and the time required by the accomplishment of recrystallization is long, but recrystallized microstructure is fine and homogeneous. When the profile is annealed at 250°C for 4h, average recrystallized grain size is 15μm.

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.

Wrought magnesium alloys for structural applications

Wrought magnesium alloys are of special interest as lightweight structural components as a result of their more homogeneous microstructures and improved mechanical properties compared to cast components. Extrusion as a shaping technology offers the possibility to produce a wide variety of magnesium alloy profiles. In this contribution, the authors describe the role of extrusion parameters such as extrusion rate, ratio and temperature as well as the type of extrusion process on the microstructure of AZ series magnesium alloys and the resulting mechanical properties. The effect of microstructure on the tensile/compression deformation behaviour of the alloys has also been investigated. In a further step, extruded material has been used in die forging experiments. Aspects of alloy development and process optimisation designed to overcome technical and economic limitations and thus establish magnesium alloy profiles for industrial applications will also be discussed.

Finite Element Simulation of Magnesium Extrusion to Manufacture a Cross-Shaped Profile

At present, a fundamental knowledge of the thermal and mechanical interactions occurring during the extrusion of magnesium is lacking. This acts as a serious technological barrier to the cost-effective manufacturing of lightweight magnesium alloy profiles. In the present research, a three-dimensional finite element (FE) simulation of extrusion to produce a magnesium alloy profile with a cross shape was carried out as an efficient means to gain this understanding. It revealed the redistribution of temperatures in the billet throughout the process from the transient state to the steady state, the formation of the deformation zone and dead metal zone, and varying fields of effective stress, effective strain, effective strain rate, and temperature close to the die orifice. The predicted extrudate temperature and extrusion pressure were compared with experimental measurements. The key to controlling the extrudate temperature and extrusion process was found to lie in the capabilities of predicting the temperature evolution during transient extrusion, as affected by extrusion conditions. The relationship between ram speed and the extrudate temperature increase from the initial billet temperature was established and experimentally validated.

Research on Technology and Microstructure Performance in Profile Extrusion of AZ31 Mg-Alloy

Aimed at characteristics of the profile such as complex shape, high dimensional accuracy and mechanical properties, the reduction zone length and devided flow taper of female die were designed by FEM and extrusion experiments were carried out for as-cast AZ31 magnesium alloy. Technological parameters were determined and microstructure and properties of the extruded profile were examined. The results show that magnesium alloy profile can be extruded if technological parameters such as deformation temperature, tool temperature and ratio of extrusion are controlled strictly. Each of the above mentioned technological parameters has its different influence on microstructure and properties of extruded profile. In comparison with as-cast alloys, microstructure is refined from 120～140μm to about 10μm and tensile strength is enhanced from 171～200MPa to above 260Mpa. This suggests that fine grain and high strength are attained for AZ31 magnesium alloy by extrusion deformation. The extruded profile can meet high properties demands for carrying parts. It provides a possibility for broader usage of magnesium alloy profiles.