Zhao Ming Liu

Effects of Hot Extrusion and Heat Treatment on Mechanical Properties and Microstructures of AZ91 Magnesium Alloy

The effects of heat treatment on the microstructure, tensile property and fracture behavior of as-extruded AZ91 magnesium alloy were studied by OM and SEM. The results show that the grain of as-cast AZ91 alloy is refined by extruding and dynamic recrystallization, and the mechanical properties increase obviously. The ductility is significantly enhanced after solution treatment of the as-extruded AZ91 alloy, tensile strength is almost the same before and hardness is significantly reduced after solution treatment and artificial aging treatment. The tensile strength reduced and the ductility is significantly enhanced of as-extruded AZ91 magnesium alloy after annealing processes. The fracture surface of as-extruded AZ91 magnesium alloy has the mixture of ductile and brittle characteristic. But after T6 or annealing treatment, its dimple number increases evidently.

Sound Insulation Study on Mg Sheet and Mg Honeycomb Panels

The sound insulation experiments were conducted to magnesium alloy sheet and magnesium honeycomb panels. It is found that the sound insulation coefficient (transmission loss, TL) of honeycomb panel is higher than that of the sheet in full sound frequency spectra, and TL spectra of both single sheet and honeycomb panel is similar with the sound frequency, thus the TL is increased obviously with the frequency. Comparably, TL of honeycomb panels is always higher than that of the sheets, especially at middle range of frequencies 6 kHz~10 kHz, the sheet has a TL of 27 to 31dB, and the honeycomb panel has 34-39 dB. The parameters of honeycomb cores is discussed briefly.

Comparative Study on Compression Deformation Behaviors of Cast and Extruded AZ31 Alloys

Compression properties, microstructure evolution and deformation behaviors of cast and extruded AZ31 alloys are investigated. The results show that compressive yield stress, ultimate strength and ultimate compression ratio between extruded and cast AZ31 alloy are quite different. The yielding pattern of as-cast AZ31 alloy is continuous, and the yield pattern of extruded AZ31 alloy demonstrate an obvious yielding plateau mode. The angle between the fractures and specimens axis of as-cast and extruded AZ31 alloy is about 45°. A mass of reliefs and damage can be found on the specimen surface of as-cast AZ31 alloy and the twinning is main deformation sign in as-cast AZ31 alloy as seen a rough surface. The slip activity might be a predominant deformation mechanism in extruded AZ31 alloy judged by smooth surface after fracture.

Effect of Pre-Strain on Fatigue Behaviour of AZ31 Mg Alloy

Mg Alloys Are the Lightest Structural Alloys with Excellent Castability and Machinability as Well as Highest Specific Strength and Stiffness. According to their Hexagonal close Packed Crystal Lattice there Is an Urgent Requirement of Mechanical Property Evaluation Method for Industrial Application, Particularly to Wrought Mg Alloys. Cyclic Loading Is a Very Popular Mode for Most Structural Application Situations. Recent Development of Fatigue Examination of Extruded Profile Has Shown that Mg Alloys Show Not so Ideal Fatigue Property. so that the Further Detailed Study on Cyclic Loading for Plastic Deformed Mg Alloys Is Needed. Tension-Tension Fatigue Tests Were Conducted on Pre-Strained AZ31 Mg Alloys that Produced by Rolling and Extruding Procedures. the Results Show that the Compressive Plastic Deformation Leads to Reduction of Fatigue Life/limit Significantly. SEM Analysis on Fatigue Fracture Surfaces Indicates that the Fatigue Cracks Initiate in the Surface or Sub-Surface of Dramatically Deformed Zones. the Microstructure Analysis Reveals that the Pre-Strain Brings More Abundant Twinning Bands with the Increase in Pre-Strain. the Decrease in Fatigue Life Demonstrates Also some Critical Feature with the Pre-Strain Level.

Study on Compression Behaviour of AZ31 Magnesium Alloy at Room-Temperature

The microstructure, surface morphology, compression properties, deformation behaviour and strain hardening exponent of as-cast and as-extruded AZ31 Mg alloy after different annealing treatments were investigated. The results show that the compression properties are great different between cast AZ31 alloy and extruded AZ31 alloy. Extruded AZ31 alloy is discontinuous yield and on the surface no signs of damage have been observed; on the contrast, cast AZ31 alloy is continuous yield and shows wavy patterns, and the surface cracks can be easily found. In addition, there is a linear relationship between the strain hardening exponent in first deformation stage and the yield ratio. Further more, the twinning mechanism plays very different role in cast AZ31 alloy and extruded AZ31 alloy.

Damage Study on AZ31 Mg Alloy under Bending Load

The microstructure, mechanical properties and damage morphology of as-cast and as-extruded AZ31 Mg alloy under different annealing treatments were investigated. The result of three-point bending test showed that the as-extruded magnesium alloy after annealing treatment followed by 300°C×30min can obtain a good mechanical properties and fine uniform grains. There are clear surface macro-cracks and emboss, the micro-cracks and cavities generated in the vicinity of the main crack, the main cracks of as-extruded samples arises from the maximum compressive stress position ,but as-cast samples arises from the maximum tensile stress position. The main crack of magnesium alloys is extended from the edge to the center of the specimen. This is because the crack propagates along grain boundaries or twin boundaries, and the cracking process will be obstructed by dislocation and/or the second phase particles

Effects of Semi-Solid Isothermal Treatments on Microstructures of Quasicrystal Reinforced AZ91 Alloys

The as-cast and semi-solid microstructures of quasicrystal reinforced AZ91 alloys were investigated. The results show that the main phases of as-cast AZ91ZY1 and AZ91ZY2 alloys are all α-Mg, I-phase, Mg17Al12 and Al2Y phase. The grain boundary phases contents increase with increasing Y and Zn contents. The better semi-solid processing technological parameters of AZ91ZY1 and AZ91ZY2 alloys are 580 °C, 30 min and 560 °C, 30 min respectively. The better semi-solid processing temperature of AZ91ZY2 alloy is lower than the one of AZ91ZY1 alloy is mainly attributed to the higher contents of the grain boundary phases in the AZ91ZY2 alloy.

Evaluation on Vibration Property of Magnesium Honeycomb Panels

The vibration and acoustic transmitting experiments and digital simulation were carried out on AZ31 magnesium sheet and magnesium honeycomb panels. The results show that the vibration characteristics and acoustic transmission loss (TL) of honeycomb panel are related to magnesium sheet and honeycomb core parameters. In full audible frequency spectra, TL of various honeycomb panels behaves in a similar manner, and the TL increases with the frequency at higher frequency. Damping enhancements of honeycomb panels contribute better vibration insulation. Vibration analysis shows that the dangerous positions are located in no-strutting areas.

Microstructures and Mechanical Properties of Mg-Al-Zn-Y Alloys

The microstructures and mechanical properties of quasicrystal reinforced Mg-Al-Zn-Y alloys with different Y and Zn contents were investigated. The results show that I-phases and Mg17Al12 phases form in all alloys. When Y content exceeds 1.0 at.%, the blocky Al2Y particles form, and it is disadvantageous to improve tensile strength and elongation rate. The tensile failure modes of Mg-Al-Zn-Y alloys are quasi-cleavage fracture. The tensile strength and elongation rate increase firstly and then decrease with increasing Y and Zn contents. When Y content reaches 1.0 at.%, the tensile strength and elongation rate achieve the highest values.

A Surface Melting Infiltration Study on Cast Magnesium Alloy

A new technique has been developed by infiltration during casting process to AZ91D magnesium alloy part. Through a melting process a alloyed surface layer was formed on the surface of the part in casting process, and the surface layer helps improve the corrosion resistance. The macro morphology, thickness, microstructure and properties of the layer were analyzed by digital, scanning electron microscopy, spectroscopy and corrosion measurement system. The results show that a uniform and dense infiltration layer on the surface of AZ91D part was obtained. This technique can fundamentally change the physical and chemical properties of magnesium alloy parts. More importantly, it is low-cost, green and environmental protection.