Hao Wei Wang

The Constitutive Model and Processing Map for In Situ 5wt% TiB2 Reinforced 7050 Al Alloy Matrix Composite

This study investigated the constitutive flow behavior and hot workability of in-situ 5wt% TiB2 reinforced 7050 Al alloy matrix composite by hot compression experiments. Based on the experimental results of flow curves, a constitutive model describing the relationship of the flow stress, true strain, strain rate and temperature is proposed. Substantially, it is found the constitutive equation of flow stress is dependent on the strain, strain rate and temperature. The coefficients (E.g., α, n, Q and lnA) in the equation are functions of true strains. The results of the calculated values from constitutive equation are verified to well agree with the experimental values. Furthermore, the processing map of the composite is created in order to determine the hot processing domains. The optimum zones for hot workability and instability regions are identified. In instability domain, the microstructures display the main failure modes as the particle cracking and interface debonding.

Anodic Alumina Oxide Template with Branched Structure Formed in Phosphoric Acid

Anodic alumina oxide (AAO) templates with multi-branched structure were fabricated in a phosphoric acid. Atomic force microscope (AFM) was utilized to investigate the unstable growth of porous oxide film in initial stage. The morphologies of cross-section of AAO templates at different current density were also studied with FESEM. The results show that the acquired AAO templates are of multi-branched structure with large size. The diameter of pores on outer surface ranges from 150 to 220 nm, and the width of branches from 100-120 nm. This structure can be due to the unstable growth of AAO film in initial stage. Besides, the structure of AAO template is sensitive to the current density and the order degree decreases with the increase of current density: at 1.0A/dm2, most of tubes are not straight and some divided into two branches; at 2.0A/dm2, all tubes grow disorderly and form net-like structure. In this electrolyte, different types of structure of AAO templates can be acquired by adjusting current density, which may be used for the synthesis of new types of nanowires with improved mechanical properties.

Tensile Properties of 15wt. %TiB2/7055 Composite Fabricated by In Situ Method

7055 aluminum alloy reinforced with 15wt. % TiB2 particulates was synthesized by in situ method, the microstructure and tensile properties were investigated. There are a few particulate clusters in the matrix. The elastic modulus and hardness of the composite are higher than that of the matrix alloy, but the yield strength and ultimate tensile strength decrease. The decrease of strength is attributed to the presence of TiB2 particulate cluster and residual reaction slag.

A New Technology to Improve the Elongation of A356 Alloy

A356 alloy was widely used in automobile industry due to its excellent castability and comprehensive mechanical properties. But, with increasing demands of strictly safety of components, fatigue life of A356 alloy became the key properties which were considered seriously. To evaluate the time-consuming properties, elongation, as a replaced property, was employed for its easy testing and the relationship which was proportional to the fatigue life of materials. Semi-solid processing was proved that it can improve the elongation of materials while the mechanical properties still kept at the same level as original alloy. Presently, many semi-solid techniques were developed to produce various products, in which the additional equipment was necessary to form the semi-solid microstructure. Therefore, this work is aimed to development an easily technique to obtain the semi-solid microstructure. In present study, A356 alloy with typical semi-solid microstructure was obtained by addition of RE elements during melt processing. In addition, the melting and pouring process was kept the same as the normal gravity casting of A356 alloy. After the treatment, the elongation was 19.5% for A356 alloy with RE addition, which was much higher than that of 13% for normal A356 alloy. Microstructure observation showed that the morphology of Si was changed significantly, and the shape of spheroid was dominantly appeared other than short rod shape. The improvement of elongation was attributed to the morphology change of α-Al and eutectic Si.

Impact Properties of Particulate Reinforced Aluminum Matrix Composites

TiB2 particulate reinforcing 7449 aluminum matrix composites were fabricated by in situ method. Their microstructure and impact properties were investigated. The impact toughness decreases with the increase of the weight fraction of the particulate whereas the hardness of the composites increases. The decrease of impact toughness could be accounted for the particulate cluster and brittle clusions. The increase of the hardness is due to fine grain size and high dislocation density.

The Role of Fe on the Grain Refinement of High Purity Aluminium

The role of Fe on the grain refinement of high purity aluminium (HPAl) was investigated after adding commercial Al-5Ti-1B grain refiner rod. Experimental results show that with a 0.08% Fe addition, the grain structure at chill zone of the HPAl sample changes from coarse to fine equiaxed grains. More importantly, the grain size observed at the centre of the HPAl sample decreased from 500±50µm to 206±30µm. The improvement has been attributed to the interfacial segregation and solute concentration of the Fe at the solid-liquid interface.

Effects of Particle Volume Fraction on Dynamic Deformation Behaviors of B4C Reinforced Aluminum Matrix Composites

Particles size grading method was employed to fabricate aluminum matrix composites reinforced with 75% volume fraction B4C particles by squeeze casting. Dynamic behaviors of the composite was investigated and compared with 55 vol. % composite which were reinforced with particles of uniform size. The results showed that the flow stress increased but the fracture strain decreased with increasing reinforcement volume fraction. Furthermore, the dynamic behaviors of 55 vol. % composite were significantly affected by adiabatic heating softening which was demonstrated by the local melted matrix on the fracture surface and an increase-decrease tendency on flow stress and failure strain was obtained with increasing impact velocity. However, due to load redistribution caused by particles size grading, no melted region was found on the fracture surface and no increase-decrease tendency on flow stress and failure strain was observed for 75 vol. % composites under the same impact loading.

Bending Properties of AA7055 Aluminum Alloy Reinforced with In Situ TiB2 Particles

In-situ TiB2 particles reinforced AA7055 composites were fabricated through mixed-salts route and their bending properties were studied. The composites reinforced with 5 wt % and 10 wt% TiB2 exhibit higher bending strength than the unreinforced matrix alloy. The improvement in bending strength may be attributed to dislocation strengthening, Orowan strengthening, and grain strengthening. The good bonding between the reinforcements and the matrix also plays an important role.