Effect of low-frequency electromagnetic field on the as-cast microstructure of a new super high strength aluminum alloy by horizontal continuous casting
The super high strength aluminum alloy ingots with 100 mm in diameter were cast by the process of low-frequency electromagnetic horizontal continuous casting (LFEHC) and the effect of electromagnet ic field on the as-cast microstructure was studied. Results show that microstructure of the sample prepared by the LFEHC process was greatly refined. Microstructures at the border and the center of the ingots were fine, uniform and rosette-shaped. Electromagnetic frequency plays a key role in microstructure refining. Fine and uniform microstructures can be obtained with optimal electromagnetic frequency. In this experiment, under a frequency of 30 Hz the microstructure was the finest and the most uniform.
Influence of Microstructural Characteristics on the Dynamic Properties of Aluminum Alloys. Influence of Distribution of Second-Phase Particles in Aluminum Alloys.
There are certain kinds of microstructural characteristics such as second-phase particles, solute atoms, grain size and grain orientation, which affect the impact strength of aluminum alloys. In this paper we discuss the influence of distribution of second-phase particles in various commericial Al-Mg-Si system alloys. Test alloys were prepared with five kinds of heat treatment : T4, under aging, T6, over aging and O temper. The deformation behavior of these alloys was investigated using a compression test at room temperature. Dynamic tests (4×102∼2×103s-1) were performed using a Hopkinson pressure bar system, and static tests (1×10-3∼1×10-ls-1) were performed with an Instron machine for reference. It has been revealed that strain rate sensitivity of flow stress varies with the interaction between second-phase particles and dislocations.
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.