Zhen Hua Chen

A Novel Spray Deposition Technology for the Preparation of Aluminum Alloy and Aluminum Alloy Matrix Composite Rings with Large Dimensions

A novel spray deposition technology with characteristic of the movable crucible, has been developed to prepare aluminum alloy and aluminum alloy matrix composite rings with large dimensions. The influences of process parameters on the microstructure and properties of the as-deposited rings were systematically investigated and the process parameters were optimized. Up to now, 7075Al/SiCp and A356/SiCp composite rings with the outer diameter of 1200mm, the inner diameter of 600mm and the thickness of 250mm, and LF6 aluminum alloy ring with the outer diameter of 3500mm, the inner diameter of 3100mm and the thickness of 250mm have been produced respectively. All the as-deposited performs were featured with the grain size about 3~5µm and a homogeneous distribution of ceramic particles the cooling rate up to 104K/s. Moreover, no cracking occurred in the performs because of the lower inner stress. The experimental results indicated that this novel technology was a promising and viable mean for the preparation of metal rings.

Advanced Plastic Processing Techniques for the Densification of Spray Deposited Preforms

In the present investigation, several novel techniques including sequential motion compaction, ceramic rolling and frame-confined rolling have been developed to improve the formability of spray deposited porous aluminum alloy preforms. The experimental results show that these techniques can greatly improve the workability of the spray deposited performs. Especially, sequential motion compaction can be used to densify the preforms of large dimensions which are difficult to further processing by the traditional techniques to fully dense.

Effect of different processes on the microstructure and mechanical properties of the Al-8.5Fe-1.3V- 1.7Si/SiCP composite sheet

Processes of rolling after extruding and rolling after hot-pressing of multi-layer spray deposited Al-8.5Fe-1.3V-1.7Si/SiCP, and the effect of the two different processes on the microstructure and mechanical properties of the composite were investigated. The microstructure of the composite prepared by different processes was observed by OM, SEM and TEM. The results showed that more uniform microstructure and more excellent mechanical properties of the composites were obtained by rolling after hot-pressing than rolling after extruding. The excellent mechanical properties can be attributed to avoiding of SiC particles lamination which is familiar to the composite as-extruded by hot-pressing, stable microstructure, and good bonding between SiC particles and the matrix.

Preparation of Nano-Particles of Metal Oxides via a Novel Solid-Liquid Mechanochemical Reaction Technology

Nano-particles of metal oxides Mn3O4, Cu2O, Fe3O4, the mixture of Zn(OH)2 and ZnO have been successfully prepared via a novel solid-liquid mechanochemical reaction technology. The metal powders are ground in water solutions using planetary ball mill. The solid-liquid reactions can occur on the surface of the powders and the reacted layer can be continuously peeled off during milling. The mean sizes of the as-prepared particles are approximately 20~100nm.The formation of nano-particles is attributed to the reactions between particles and solution as well as the repeated and quick peeling of the formed oxides on the surface of metal particles. Furthermore, the reaction rate and phase types of the products can be controlled by adjusting the pH value of the solution.

Evolution of SiC Particle Distribution in Spray Codeposited SiCp/ 7075 Al Composites during Extrusion

The evolution of SiC particle distribution in spray codeposition SiCp/7075Al composite during extrusion was investigated. A unique metallurgical pattern designated as ring- and band-pattern in the cross section of the extruded products occurred which comprises areas with higher and lower concentrations of SiC particles. The factors that contributed to the evolution of SiC particles distribution feather during plastic deformation were analyzed. The difference of flowability between the matrix and SiC particles was supposed to be the main factor accounting for the forming of the ring- and band-pattern. In addition, concentration difference of SiC particles between different deposition layers will also contribute to the forming of the ring- and band-pattern. A simple model was proposed to describe the evolution of SiC particle distribution during extrusion.

A Novel Method for Sheet Formation of Porous Spray Deposited Al-Fe-V-Si Alloy Reinforced with SiC Particles

Processes of rolling after wedge pressing and extruding for multi-layer spray deposited Al-Fe-V-Si/SiCP sheet formation were described in this paper, and the effects of the two different processes on the microstructure and mechanical properties of the composite were investigated. The microstructure of the composite prepared by different processes was observed by OM, SEM, and TEM. The experimental results show that the wedge pressing process can obviously eliminate the pores in the as-deposited preforms and improve the formability effectively. And more uniform microstructure and more excellent mechanical properties of the compositesheets were obtained by rolling after wedge pressing than that by extruding. The excellent mechanical properties can be attributed to avoiding of SiC particles lamination and aggregation which are familiar to the composite as-extruded. Stable microstructure, and good bonding between SiC particles and the matrix improve its mechanical properties further.

Microstructures, Mechanical and Creep Properties of Rapidly Solidification/Powder Metallurgy Mg-6wt.%Zn Alloys with 5wt.%Ce and 1.5wt.%Ca Additions

Rapidly solidification/powder metallurgy (RS/PM) Mg-6Zn, Mg-6Zn-5Ce and Mg-6Zn-5Ce-1.5Ca (wt.%) alloys were produced via hot extrusion with RS powders, produced by atomization-twin roll quenching. Microstructures, mechanical and creep properties of the alloys were investigated. The results showed that for the Mg-6Zn alloys with 5wt.%Ce and 1.5wt.%Ca additions, the microstructures of the alloys were gradually refined, which caused the strength of the alloy at room temperature to increase remarkably, especially for the RS/PM Mg-6Zn-5Ce-1.5Ca alloy, exhibited a high compressive strength of 394MPa at room temperature. At elevated temperatures, due to the fine and stable intermetallic compounds i.e. MgxZnyCez and MgxZnyCez-(Ca) phases were formed for the Mg-6Zn-5Ce alloy and Mg-6Zn-5Ce-1.5Ca alloys, respectively, and the thermal stability of the ternary phase was a little lower than that of the quaternary phase because of the dissolving of Ca into the MgxZnyCez phase, the mechanical and creep properties at elevated temperatures increased remarkably with Ce and Ca additions, especially for the RS/PM Mg-6Zn-5Ce-1.5Ca alloy, which exhibited a high compressive strength of 258MPa at 200°C, and the minimum creep rate was decreased about 2 times, compared with that of the Mg-6Zn-5Ce alloy.

Some Studies on Preparation of Large Spray Deposited Aluminium Alloy Tube Preform

In this paper, preparation of large spray deposited aluminum alloy tube was investigated. The shape and particle size distribution of over-sprayed powders together with structure of deposits were analyzed. The results show that the over-sprayed powders resulted from particles missing, spurting and rebounding. The particle size distribution was non-standard normal distribution, the particle size of the great majority was within 150μm and the average size was 50μm. The residual pores in deposits came into being when inter-particle space could not be filled with enough liquid during spray deposition. The as-deposited preform with rough surface was a coalesced bulk of deposited particles. The rotate speed of substrate and scan speed of atomizer together with spray stripe width should satisfy any certain relationship to obtain a qualified tube preform. Substrate preheating and surface treatment and residual stress control were very important for preparing a large preform.

Enhanced Formability of AZ31 Magnesium Alloy Sheet Processed by Equal Channel Angular Rolling and Annealing Treatment

In order to improve the formability of AZ31 magnesium alloy sheet at room temperature, a new process, so-called equal channel angular rolling (ECAR) and followed by annealing treatment was applied to process the sheet. The optical microstructure of the as-received sheet was similar with that of the ECARed one after annealing treatment, the Erichsen value and limiting drawing ratio of the ECARed sheet was about 6.26mm and 1.6, respectively, which was much larger than that of 4.18mm and 1.2 for the as-received sheet. These can be attributed to the low yield ratio and high strain hardening exponent due to the modified texture induced by the shear deformation during ECAR process, which is favor of the activations of basal slipping and twinning at ambient temperature, especially deforming at the rolling direction.