Materials Science Forum Vols. 618-619

Abstract: Within the project “Advanced Processes for Hybrid Metal/Plastic Products” which is part of the Cluster of Excellence “Integrative Production Technology for High-Wage Countries”, established and financed by the German Research Foundation (DFG), new hybrid processes for the production of metal/plastic-composites will be developed. The activities of the Foundry Institute focus on the processing of structural parts with excellent mechanical properties and special integrated functions by combining two original mould operations. In the long term, the metal/plastic-composites are to be produced in a single step process, using one mould and one machine. Beside the combination of the two processes, high pressure die casting and injection moulding, preliminary test geometries will be manufactured in separate moulds. The operation using the two moulds consists in the production of the aluminium metal part in a pressure die casting mould, and subsequently the injection of the plastic component into an injection mould. The basics needed to define the adhesion mechanism between metal and plastic were investigated under experimental conditions in order to determine appropriate results for tests, carried out under the process conditions of high pressure die casting. It is proposed to find and to develop new concepts to join these two different materials. The best bonding mechanism will be chosen to obtain the first metal/plastic hybrid products in the so-called One-Step-Process. A selection of promising results concerning the bond strength of different joining concepts under application terms are presented in this paper.

Abstract: Two new AZ31 nanocomposites containing Al2O3 nanoparticle reinforcement were fabricated with different reinforcement integration methods using solidification processing followed by hot extrusion. Each nanocomposite had similar composition (Al and Zn contents), microstructure (grain and intermetallic particle sizes, Al2O3 nanoparticle distribution) and hardness. However, the first nanocomposite had better overall tensile properties compared to the second nanocomposite. Also, the second nanocomposite exhibited better overall compressive properties compared to the first nanocomposite. On the whole, the second nanocomposite was more deformable in tension and compression than the first nanocomposite. The effect of reinforcement integration method on the tensile and compressive properties of the AZ31- Al2O3 nanocomposites is investigated in this paper.

Abstract: A two-stage process in the formation of TiAl3 was found in the accumulative roll bonding (ARB) Ti/Al multilayers. The distribution of layer spacing did not become broad enough to lose the main features of the double exothermal behaviour. A modified model based on thin films was set up to describe the kinetic characteristics of the formation of TiAl3 in ARB samples

Abstract: The parameters of ultrasonic processing have important effects on the distribution and dispersion of nano-sized particles in magnesium matrix nanocomposite (MMNC) fabrication. In order to learn more about the above effects and produce guidelines for the fabrication of MMNC, the acoustic cavitation and streaming effects produced by high intensive ultrasonic method with different frequency and power were experimented with water, glycerol, soybean oil and oil-water mixture respectively. The results showed that the acoustic cavitation and streaming were influenced by ultrasonic frequency and power as well as the depth of waveguide dipped into melts. The ultrasonic processing of the MMNC melts with 20kHz and 1.4kW greatly improved the dispersion and distribution of nano-sized reinforcement particles in MMNC.

Abstract: Vickers and nano indentations were performed on a structurally relaxed Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG), and the evolution of the shear bands in the relaxed BMG was investigated and compared to that in the as-cast alloy. Results indicate that the plastic deformation in the BMG with structure relaxation is accommodated by the semicircular (primary) and radial (secondary) as well as tertiary shear bands. Quantitatively, the shear band density in the relaxed alloy was much lower than that in the as-cast alloy. The annihilation of free volume caused by the annealing was responsible for the embrittlement of the sample with structure relaxation.

Abstract: SiC particles are effective grain refiners in Mg-Al alloys. Several investigations, from different researchers, into their effect on a range of alloys with different Al contents has been undertaken and it has been found that the greatest reduction in grain size occurs in alloys having low Al contents. Performing grain refinement studies on a range of alloy contents also allows for further investigation into the mechanisms of grain refinement. It was found that the size of the SiC particles is also important in magnesium grain refinement. However, the presence of Mg2Si in the microstructure and the consideration of phase equilibria suggest that SiC can transform into other binary or ternary carbides. If such carbides are formed, they may also act as an effective grain refiner for Mg-Al alloys. In this study, the possibility of formation of new carbides (Al4C3, Al2MgC2, Mn7C3, Mg2C, Mg2C3, Al2CO etc.) and their ability to be good grain refiners for Mg-Al alloys is discussed.

Abstract: A high intensity ultrasonic assisted casting method was used to fabricate SiC nanoparticles reinforced magnesium matrix nanocomposites (n-SiCp/AZ91D). The microstructures and mechanical properties of the nanocomposites were investigated. The results show that n-SiCp are well dispersed in the matrix and the grain size was refined. A HRTEM study of the interface between n-SiCp and the matrix suggests that SiC bonds well with matrix without forming an intermediate phase. With the lower addition of n-SiCp, the mechanical properties of nanocomposites are greatly improved. As compared to an unreinforced magnesium alloy matrix, the tensile and yield strength were improved by 43.6% and 117% respectively.

Abstract: This paper presents an analysis, based on microstructural observations by transmission electron microscopy, of the influence of chemical composition on creep resistance of high pressure die casting (HPDC) Mg-4RE-0.6Zn alloys. The improved creep resistance, by increasing the Nd/La ratio of the rare earth (RE) mixture, is shown to be associated with the supersaturation of Nd solute in the -Mg matrix, evidenced by the formation of Nd-rich precipitates on dislocations after a thermal ageing treatment. The result indicates that solid solution/precipitation strengthening of the -Mg matrix is important to the creep resistance of HPDC Mg-RE based alloys.

Abstract: The increasing use of heat resistant magnesium alloys for automotive applications is expected to influence the chemical composition of upcoming post consumer scrap. Therefore it would be useful to define alloys that resemble the future composition of the material. For this purpose a matrix of potential recycling systems has been set up. AM50 was used as a base material to which decisive amounts of strontium, silicon and calcium were added. The basic heat resistant alloy systems AJ, AS, and AX have been investigated closely. This work deals with combinations of the three above mentioned elements. Some essential observations shall be presented concerning the development of the microstructure and its influence on the materials properties. For combined additions of strontium, silicon and calcium the formation of a new ternary phase has been observed. The compound has a positive influence on the fracture elongation and the corrosion rate in the salt spray test.

Abstract: Room temperature formability of twin-roll cast Mg alloys has been investigated and correlated with their work hardening behavior. Tensile properties of these alloys were measured and their work hardening behaviour was analysed by using constitutive equations. Room temperature formability of the alloys was evaluated by the limiting dome height (LDH) value, obtained by the Erichsen cupping test. It shows that there is a linear relationship between LDH value and the inverse of yield ratio, which is a function of work hardening exponents. An increase in grain size increases work hardening exponent and concurrently increases LDH.