Materials Science Forum Vols. 546-549

Abstract: A new method has been devised to obtain a Zn coating on the AZ91D magnesium alloy from the base electrolyte of ZnSO4 and K4P2O7 by electroplating. To improve the properties of the coating, a SnO2 sol was prepared and added in the electrolyte. The effects of the SnO2 sol addition on the morphologies, compositions and phase structures of the plated coatings were investigated by scanning electron microscopy (SEM), energy dispersion spectrometry (EDS) and X-ray diffraction (XRD). The results reveal that the addition of SnO2 in the solution changes the polarization behavior of the electrolyte and the compositions of the plated coating. The plated coating formed in the electrolyte with an addition of SnO2 sol are more uniform and provide a better protection for the AZ91D substrate.

Abstract: In this paper, the solution mainly containing Zn(H2PO4)2 was used to prepare phosphating coatings on AZ31,AZ61 and AZ91 magnesium alloys. The effects of the phosphating parameters and the composition of phosphating solution on the formation of the coatings were investigated by orthogonal tests. The corrosion behaviors of the phosphating coatings were also studied and it is found that there was no hydrogen evolution in at least 1h. In the last, 60~80μm organic coatings were painted on the phosphated magnesium alloys,the organic coatings adhered to the phosphating coating, and the anti-corrosion abilities were improved .

Abstract: The specific gravity and elastic modulus of magnesium alloys are similar to that of human bone. Magnesium is one of the most important elements in the human body and plays a key role in the metabolic process. But the application of magnesium is seriously limited as a biomaterial since it corrodes easily in the physiological environment of the body. In order to reduce the corrosion, we developed protective films using rare earth (RE) conversion processing. The surface of magnesium samples was modified by contact with different rare-earth salt solutions; then the samples were dipped in SBF to test their corrosion resistance. The change of mass and the pH of the solutions were measured continuously using an electronic scale and a pH micrometer. The surface microstructure of the samples was observed by XRD and metallomicroscope. Corrosion rates of the samples in SBF were determined using Taffier curve. The preliminary results show that the conversion treatment with CeCl3 or Y(NO3)3 can improve the corrosion resistance of magnesium in SBF. The relationship of the RE salts concentration and the corrosion properties were studied,the best combination of parameters was determined, and the formation mechanism of rare-earth conversion film has been also elaborated.

Abstract: Aluminum boron carbide particulate reinforced composites are advanced materials which have superior mechanical properties, and especially have the capability to capture neutrons. The liquid mixing process is one of the methods to produce economically and effectively the metal matrix composites. However, it was found that the fluidity of the composites was instable during liquid holding and casting. To examine the fluidity evolution over the time, the melt of an Al-10%B4C composite was hold at a constant temperature for a long period, and the fluidity was evaluated by means of a vacuum fluidity test. The microstructure of the fluidity test samples was examined by optical and electron microscopes. It is found that the interfacial reaction products between B4C and Al-matrix play an important role for the deterioration of the composite fluidity.

Abstract: Vacuum infiltration is one of the composite production method. Reinforcement volume ratio, vacuum value, molten matrix composition and temperature, infiltration atmosphere and time are important parameters in infiltration of molten metal into preformed reinforcement. In this study, MgO powder and Al were used as reinforcement and matrix respectively. Mixture of MgO and Al powders with –105 μm particle size were filled in quartz tubes freely to form 30 % reinforcement volume ratio. Liquid pure Al with varying Mg contents were vacuum infiltrated into the MgO powder under 550 mmHg vacuum at two different temperatures in normal atmosphere for 3 min. After vacuuming, infiltration height and density of produced composite have been determined. Fracture behavior of composites has also been determined by three point fracture test. Microstructure of composites and fracture surface were investigated by SEM analysis. It has been found that fracture strength of composites decreased although infiltration height and density increased with increasing Mg content of liquid Al. It has been also determined that molten metal temperature facilitates infiltration.

Abstract: The strength of aluminum alloys was improved by a severe deformation process while the decrease of elongation leads to the defect. Modification of A3003 alloy was attempted in order to develop a high strength and high formability Al alloy tube for the application of air-conditioning systems in transportation, such as passenger planes and automobiles. An A3003 alloy was modified by Ti addition, grain refiner. As a result of modification, the modified A3003 alloy was able to suitably satisfy the mechanical strength requirements, including elongation. Grain size and secondary dendrite arm spacing of A3003 alloy decreased by as much as 50 % by Ti addition. The finer grains were uniformly distributed in the modified A3003 alloy billet. The yield strength of the modified A3003 alloy was improved by 30 % without decreasing elongation.

Abstract: Effect of Si on the forming ability of quasicrystalline phase in Al65Cu20Fe15 alloys fabricated under conventional casting conditions has been studied using X-ray diffraction (XRD), optical microscopy (OM), and scanning electron microscopy (SEM). The results show that under the conventional casting conditions, it is found that the addition of certain amount of Si into the Al-Cu-Fe melts can change the formation of Al62.5Cu25Fe12.5 quasicrystals during the solidification process. Compared with Al65Cu20Fe15 alloy, Al64.5Cu20Fe15Si0.5 alloy has smaller volume fraction of β phase solidifying initially, larger volume fraction of the quasicrystal phase generating in the subsequent peritectic reaction, and larger volume fraction of ω phase solidifying finally. Both experimental results and the theory of Hume-Rothery show that addition of Si can promote the formation ability of the icosahedral quasicrystalline Al62.5Cu25Fe12.5 phase in Al-Cu-Fe alloy.

Abstract: We have systemically studied the effect of the erbium on the microstructure and the mechanical properties in the 5xxx series aluminum alloys by using optical microscope, transmission electron microscope (TEM) and by tensile testing. The results demonstrate that the tensile strength increased quickly at the beginning of small contents of 0.1%Er both in the hot and cold rolled states, then slowly increased with increasing the contents of Er until 0.4%, at which the best balance of the strength and ductility (438MPa and 9.6%) were obtained. Microstructure observation in the hot rolled state was indicated that the grain structure in the Er free Al-5Mg alloy revealed fully recrystallized grain structure, while in the Al-5Mg containing Er was demonstrated deformation structure, indicating the Er addition delayed the recrystallization behavior by the formation of the precipitation of the Al3Er, which confirmed by means of the X-ray diffraction analysis. Furthermore in the TEM microstructure observation the precipitation of Al3Er was distributed both in the grain interior and subgrain or grain boundaries, which could be pinning the subgrain or grain boundary migration and dislocation movement as well. Consequently the beginning of the recrystallization temperature in the Al-5Mg containing Er was elevated about 50°C than in Al-5Mg without Er. This could be explained that the strength increased without the deterioration of the ductility was attributed to the microstructure refinement by the Er addition.

Abstract: The microstructures of Al-0.2Sc and Al-0.2Sc-0.12Zr alloys have been investigated.The results show that Al3Sc and Al3(Sc1-xZrx) dispersoids exist in as-rolled Al-0.2Sc and Al-0.2Sc-0.12Zr alloy respectively, and their orientation is (001)α║(001)dispersoid, [010]α║[010]dispersoid.The Al3Sc particles in as-rolled Al-0.2Sc were precipitated from hot rolling process, while the larger Al3(Sc1-xZrx) particles in as-rolled Al-0.2Sc-0.12Zr from the solidification, and the small particles also from hot rolling process. There is segregation of Sc and Zr in the Al3(Sc1-xZrx) dispersoid, and Sc is rich in the outside shell while Zr rich in the core of the particles. It is believed that the grain and subgrain boundaries can be pinned by the Al3Sc particles when annealed after cold-rolling, and this may lead to restricting the recrystallization of the Sc-containing alloys.And it’s not until the dissolution of Al3Sc that the recrystallization can happen in this kind of alloys.

Abstract: The stir-casting method was utilized in this paper to synthesize 6063Al/Al2O3·SiO2 reinforced composites consisting of 6063Al alloy as matrix and Al2O3·SiO2 particles as additive with content of 5%, 10%, 15%, 20% (volume fraction) respectively. Al2O3·SiO2 particles were obtained from fly ash particles of Steam Power Plant and were pretreated. The shape of these fly ash particles was spheroidal and ellipsoidal. The damping behavior of 6063Al/Al2O3·SiO2 particle reinforced composites was studied by measuring the composite’s internal friction values on a Multifunctional Damping Measurement Apparatus. Under the condition of this series of experiments, 6063Al/Al2O3·SiO2 particle reinforced composites had a higher internal friction values than that of 6063Al matrix and also showed the dependency of internal friction on Al2O3·SiO2 particles volume fraction, particles dimension, vibration frequency and temperature. There was an increased trend for internal friction values with increasing the volume fraction of Al2O3·SiO2 particles and decreasing particles dimension of Al2O3·SiO2 at the same frequency and the different temperature. It has been found that in the lower frequency, the higher internal friction value was obtained. The internal friction of the composites increased with increasing temperature. In the case of lower frequency, two damping peak were observed. A low-temperature damping peak appeared at a temperature near 245°C which a high-temperature damping peak appeared near 450°C. Based on the experimental results, the damping mechanism of 6063Al/Al2O3·SiO2 particle reinforced composites was preliminary discussed. It may be concluded that the damping mechanisms associated with 6063Al/Al2O3·SiO2 reinforced composites include mainly intrinsic damping, dislocation damping and interface damping. However, only the interface damping mechanism is dominant at high temperature.