Whisker-reinforced Aluminum Composite Research Articles

Profound strengthening and toughening effect of reinforcement aspect ratio in composite with network architecture

Reinforcement aspect ratio is a fundamental parameter that affects the properties of metal-matrix composites (MMCs). Here particle- and whisker-reinforced aluminum composites with network reinforcement distribution were modeled to reveal the effects of aspect ratio on the deformation and fracture behaviors and thus mechanical properties. The results showed that the modulus and yield strength exhibited a U-shaped dependence on the aspect ratio of reinforcement because the load-bearing capacity of reinforcement showed a balance between aspect ratio and local volume fraction in the network architecture. For SiCp/Al composite with network architecture, particles in network layers parallel to external load exhibited higher stress (750–1000 MPa); while in SiCw/Al, the whiskers in perpendicular layer bore higher load, which increased with the aspect ratio of the whisker. Furthermore, the fracture elongation (εfxx) of the network composites increased with reinforcement aspect ratio. SiCp/Al composite showed a smaller εfxx and brittle fracture behavior. This is contrary to the SiCw/Al network composite, which experienced a much larger εfxx and ductile fracture due to macro-interfacial decohesion behavior between SiCw rich and lean areas.

Electrochemical impedance spectroscopy characteristic of Al18B4O33w/AA6061 and the evolution of growth morphology of cerium conversion coating on its surface

Because of their good properties and low density, whiskers reinforced aluminium composites are used in the aircraft, automobile industries and marine environments. Alumina borate whisker reinforced aluminium composites attracted attention for the lower price of the whisker and excellent properties of the composites. However, they are susceptible to the corrosive medium, which limits their extensive application. Coating is an effective method to improve corrosion resistance of the composites. In this manuscript, electrochemical impedance spectroscopy measurements were performed on the Al18B4O33w/AA6061 composites with and without hydrofluoric acid pre-treatment. A similar electrochemical characterisation was exhibited on the composites with and without pre-treatment during exposure in a 3.5 wt-% NaCl solution. However, their corrosion mechanisms in the corrosion media were completely different. During the immersion process, it was noted that the corrosion resistance gradually increased for the composite with the pre-treatment and continuously decreased for the no pre-treatment one. The difference in the surface states of the composites was responsible to the change of the corrosion mechanism. Cerium conversion coating was deposited on the composites with and without pre-treatment by a conventional dip method. The formation, growth and morphology of the coatings were affected by the pre-treatment prior to the coatings.

Bending properties and fracture mechanisms of ZnO and ZnAl2O4 coated aluminium borate whisker reinforced aluminium composites

ZnO and ZnAl2O4 coated aluminium borate whisker (ABOw) reinforced pure aluminium composites were fabricated by squeeze casting. The effects of the coatings on the bending properties of the composites were investigated. On the analysis of fractographs, the fracture mechanisms of the composites under bending were also investigated. The results show that both ZnO and ZnAl2O4 coatings of ABOw can significantly increase the bending properties of ABOw reinforced aluminium composite. In ABOw/Al, ABOw/ZnO/Al and ABOw/ZnAl2O4/Al composites, the interface debonding, near interface fracture and near interface fracture and ABOw fracture dominate the fracture of each composite during bending respectively.

414 セラミック短繊維強化Al基複合材料の摩擦圧接部における熱伝導解析

414 セラミック短繊維強化Al基複合材料の摩擦圧接部における熱伝導解析

Tensile properties and fracture mechanisms of ZnO and ZnAl 2O 4-coated Al 18B 4O 33 whisker reinforced aluminum composites

ZnO and ZnAl 2O 4-coated Al 18B 4O 33 whisker reinforced pure aluminum composites were fabricated by squeeze casting. The effects of the coating contents on the ultimate tensile strength (UTS), 0.2% proof stress ( σ 0.2) and elongation to fracture ( δ) of the composites were investigated. The results show that the UTS of ZnO-coated Al 18B 4O 33 whisker reinforced aluminum composites increases almost linearly as the coating contents increase. However, the UTS of ZnAl 2O 4-coated Al 18B 4O 33 whisker reinforced aluminum composites declines initially and increases later. The ZnAl 2O 4 coating of the whiskers is more favorable for an increase in the σ 0.2 of the composites. The δ of the composites obtains its maximum value with an appropriate coating content. Fracture mechanisms of the composites were also investigated.

Effect of ZnO coating of whiskers on thermal expansion properties of aluminium borate whisker reinforced aluminium composites

The pure aluminium composites reinforced by ZnO coated aluminium borate whiskers were fabricated by squeeze casting. The microstructure of the composite was observed using an optical microscope and the thermal expansion behaviours of the composites were investigated in the range from 50 to 400°C. In addition, the effects of heat treatment and thermal cycling on the thermal expansion behaviours of the composite were also investigated. The results show that the coefficient of thermal expansion of as cast composites decreases with the ZnO coating content increasing. However, heat treatment time and thermal cycling lead to an increase in the CTE of the composite.

The effect of an interfacial layer containing nanosized Pb particles on the damping behavior in Al 18B 4O 33/Al composite

The damping behavior of Al18B4O33 whisker-reinforced aluminum composites with and without an in situ reaction layer including nanosized Pb particles at the Al18B4O33–Al interface was studied. Experimental results indicate that Pb particles at the interface between Al18B4O33 and Al alter the dislocation status of the Al matrix adjacent to the interface, resulting in a change in damping properties of the Al18B4O33/Al composites. The damping peak at medium temperature (about 150 °C) in the Al18B4O33/Al composite was ascribed to a dislocation mechanism.

Structure and hardness of surface of Al 18B 4O 33w/Al composite by laser surface melting

As a new material, aluminum borate whisker reinforced aluminum composites have attracted interest and have been considered for a wide range application because of their high specific strength, high modulus and low cost. The study included a detailed characterization of the laser melting surface in terms of microstructures, phase analysis and a ratio of Al 2O 3 (the decomposition products of whiskers during laser process) and Al in intensity with tests parameters as an indication of Al 2O 3 distribution. Microhardness of the laser layer was also studied in detail. The results indicated that the most of γ-Al 2O 3 exists at the bottom of the laser pool, which led to a maximum value in the hardness be obtained. Microhardness of the laser layer was improved to 294 Hv as compared to 178 Hv of the as-cast composite, because of the existence of Al 2O 3 particles, solid solution hardness and the grain refinement of the laser layer following rapid quenching associated with the process.

The effect of YAG laser surface treatment on corrosion resistance of Al 18B 4O 33w/2024Al composite

As a new material, aluminum borate whisker reinforced aluminum composite has been considered for a wide range applications. However, addition of reinforcements to aluminum will change the corrosion behavior significantly. A pulsed YAG laser installation was used to produce surface treatment on Al 18 B 4O 33 w /2024Al composite. Electrochemical method was used to study the corrosion resistance in 3.5% sodium chloride (NaCl) solution. The crystalline phases of the composites with and without laser surface treatment were analyzed using X-ray diffraction (XRD) measurement technique. The cross-section morphologies of the laser-treated composite were characterized by scanning electron microscope (SEM). Polarization experiments showed that the sensibility to pitting corrosion for the laser treated specimen was greatly lower than that of the untreated specimen. The reduction of reinforcement Al 18B 4O 33 whisker and intermetallics CuAl 2 on the surface of the laser-treated composite along with the formation of the homogeneous and defect free microstructure in the laser-modified layer led to improvement on the corrosion resistance of the laser-treated composite.

Internal Friction and Young's Modulus of 9Al<sub>2</sub>O<sub>3</sub> 2B<sub>2</sub>O<sub>3</sub> Whisker Reinforced Aluminum Matrix Composite

Anelastic behavior of a 9Al2O3·2B2O3 (AlBw) whisker reinforced aluminum composite has been examined through the measurements of the dynamic Young’s modulus and internal friction over a temperature range of 25 to 500°C at frequencies of 0.01, 0.05 and 0.1 Hz. A standard servo-hydraulic mechanical testing machine equipped with an infrared lamp heater was employed, but the dynamic measurement system therein was especially designed by assembling a scanning laser extensometer and a frequency response analyzer for detecting the amplitude and phase lag of strain in response to a sinusoidal time-varying stress. Two peaks of internal friction were observed over the ranges 100 to 250°C (LT peak) and 250 to 400°C (HT peak), together with marked decreases in the dynamic Young's modulus in the same temperature ranges. From a quantitative analysis of the experimental data, it is concluded that the HT peak phenomenon is due to grain-boundary relaxation, whereas the LT peak phenomenon is ascribable to the relaxation caused by stress-directed interfacial diffusion of Al atoms along the whisker-matrix interface.

Effect of changing rate of residual stress on thermal expansion behavior of magnesium borate whisker-reinforced aluminum composite

Magnesium borate whisker-reinforced aluminum matrix composite is a new aluminum matrix composite with high properties and low cost. In the study, the residual stress changing behaviors on heating and cooling of the composite were investigated through the coefficient of thermal expansion (CTE) curves. On heating, the tensile stress relaxation and compressive stress generation in the matrix of the composite results in the CTE of composite is smaller than that predicted by mixture rule, but the compressive stress relaxation in the matrix of composite causes the CTE of composite is larger than that predicted by mixture rule. The tensile and compressive stress changing rates with temperature are linear on heating in the matrix of the composite at lower and higher temperature ranges. The CTE of the composite on cooling is smaller than that on heating.

Effects of ZnO coating on the wettability and tensile properties of aluminum borate whisker-reinforced aluminum composite

A pure aluminum matrix composite reinforced by ZnO-coated aluminum borate whiskers was fabricated by squeeze casting. The effect of coating content on the whiskers/matrix wettability and tensile properties of the composite were investigated. The result shows the interfacial wettability increases with increasing coating content. The effects of coating content on the ultimate tensile strength, elongation to fracture and fracture mechanisms of the composites are also discussed.

Effect of NiO coating of whisker on tensile strength of aluminum borate whisker-reinforced aluminum composite

After NiO coating of aluminum borate whisker, the whisker-reinforced aluminum composite was fabricated by the squeeze casting technique. The effects of surface coating on the interface reaction and microstructure of the composite were investigated using transmission electronic microscope. The results indicate that the NiO on the whisker surface can react with the aluminum matrix during T4 treatment, and the degree of the reaction increases with the T4 treatment time increasing. The interfacial reaction affects obviously the tensile strength of the composite, and the suitable degree of the interfacial reaction can be found for the ultimate tensile strength.

Stress Corrosion Cracking and Hydrogen Embrittlement of Whisker-Reinforced Aluminum Composites

Abstract Stress corrosion cracking (SCC) in an 3.5% sodium chloride (NaCl) aqueous solution, hydrogen-induced cracking (HIC) during dynamic charging, and hydrogen embrittlement (HE) after precharging of whisker-reinforced aluminum composites were studied. For all four aluminum composites with the whisker direction perpendicular to the normal stress, SCC occurred but no SCC occurred if the whisker direction of Al18B4O33/Al was parallel to the normal stress. The threshold stress intensity of SCC (KISCC), measured using double cantilever beam (DCB) specimens, was (0.94 to 0.70)KIC, where KIC is the fracture toughness. The susceptibility to SCC, measured by slow strain rate test (SSRT), was 24% for SiC/Al and 13% for Al18B4O33/Al. The susceptibility to HE of Al18B4O33/Al was 44%. HIC occurred during dynamic charging under Mode II loading and the threshold stress intensity was KIIH = 0.85KIIC for SiC/Al and 0.88 KIIIC for Al18B4O33/Al, respectively. The results show that the existence of the whisker/Al interfa...

Effects of thermal residual stress creeping on microstructure and tensile properties of SiC whisker reinforced aluminum matrix composite

After quenching from 600 °C, the isothermal treatment at 80 °C for SiC whisker reinforced aluminum composite was carried out. The results indicated that the dislocation state in the matrix was changed greatly, especially in the region adjacent to the interface between SiC whisker and matrix. The change of dislocation state was considered as the result of creeping caused by thermal residual stress (TRS). It was found that the thermal residual stress creeping (TRSC) treatment is a new method to reduce effectively the TRS, and increase the strengths, including micro yield strength ( σ 0.005), yield strength ( σ 0.2), ultimate tensile strength (UTS), of SiCw/Al composite. The mechanism of TRSC of SiCw/Al composite was given in detail. After TRSC treatment for 500 h, the UTS of pure aluminum matrix composite was up to 330 MPa.

Effect of thermomagnetic treatment on tensile properties of Al 18B 4O 33 whisker-reinforced aluminum composite containing Fe 3O 4 particles

A new aluminum borate whisker-reinforced aluminum composite containing Fe 3O 4 particles was fabricated using squeeze-casting method. The microstructure and tensile properties of the composite were investigated. The results show that the thermomagnetic treatment with a pulse field is an effective technique to enhance the ultimate tensile strength and plasticity of the composite. On the basis of the analysis of broadening effect of X-ray diffraction peak, the mechanism of the effect of pulsed-field thermomagnetic treatment on the tensile properties of the composite was discussed.

Thermal mismatch stress in SiC whisker reinforced aluminium composite: new measurement method by X-ray diffraction

A new X-ray diffraction method for characterising thermal mismatch stress (TMS) in SiCw–Al composite has been developed. The TMS and thermal mismatch strain (TMSN) in SiC whiskers are considered to be axis symmetrical, and can be calculated by measuring the lattice distortion of the whiskers. Not only the average TMS in whiskers and matrix can be obtained, but the TMS components along longitudinal and radial directions in the SiC whiskers can also be deduced. Experimental results indicate that the TMS in SiC whiskers is compressive, and tensile in the aluminium matrix. The TMS and TMSN components along the longitudinal direction in the SiC whiskers are greater than those along the radial direction for a SiCw–Al composite quenched at 500°C.

Effect of annealing treatment on the stress corrosion cracking behavior of SiC whisker reinforced aluminum composite

Abstract Stress corrosion cracking (SCC) behavior of SiCw/pure Al or SiCw/2024Al composite in 3.5% NaCl solution was studied using double cantilever beam method. The effect of annealing treatment on SCC behavior of the composites was examined. The results indicated that the annealing treatment had an influence on the SCC properties of the composites. With the increase of the annealing temperature, the threshold stress intensity factor, K ISCC , increased and the steady propagation rate of SCC decreased, so that the SCC susceptibility of composites was improved.

Characterization of internal friction of Fe-30Mn-6Si-5Cr

The damping behavior of Al18B4O33 whisker-reinforced aluminum composites with and without an in situ reaction layer including nanosized Pb particles at the Al18B4O33–Al interface was studied. Experimental results indicate that Pb particles at the interface between Al18B4O33 and Al alter the dislocation status of the Al matrix adjacent to the interface, resulting in a change in damping properties of the Al18B4O33/Al composites. The damping peak at medium temperature (about 150 °C) in the Al18B4O33/Al composite was ascribed to a dislocation mechanism.

High cycle fatigue of squeeze cast AL/SiCw composites

The high cycle fatigue behavior of squeeze cast SiC whisker-reinforced aluminum composites based on either A356 Al or A390 Al matrices has been studied. Squeeze cast Al/SiCw specimens, which contain roughly 17 vol.% whiskers from two different sources, have been examined for their high cycle fatigue strength under fully reversed test conditions using a staircase method to determine the mean fatigue strength at 107 cycles. The results show 30–40% increases in the fatigue strength of the A356 Al-based composites when compared to the unreinforced matrix alloy, but much less fatigue strengthening in the A390 Al-based composites. A fractographic analysis indicates that about 80% of the composite specimens fail as a result of crack initiation within regions which are characterized by low volume fractions of the SiC whiskers. These reinforcement-free regions assume two forms: continuous ‘veins,’ which are the more deleterious to fatigue, and discontinuous ‘unreinforced areas,’ which are deleterious only in certain shapes and sizes. Both finite element analysis and an Eshelby-based analysis indicate that the localized stresses within the unreinforced regions appear to be high enough to initiate fatigue cracks, especially if unreinforced areas are elongated and their major axis is aligned to the stress axis. The fractographic analysis also identifies the importance of primary Si particles in limiting the fatigue strength of the A390 Al–based composites.