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.
A quantitative analysis of hydrogen trapping
The complex hydrogen trapping characteristics of iron-titanium-carbon alloys, contain-ing both reversible and irreversible traps have been fully analyzed. The key to this quantitative analysis is a complete identification of the type and number of each operating trap. The trapping parameters were obtained from an analysis of the relevant hydrogen permeation transients. Titanium substitutional atoms have been shown to be reversible, low occupancy traps with an interaction energy with hydrogen,E (Ti-H), of 0.27 eV. Typi-cal rate constants for these alloys are; a hydrogen capture rate constant of approximately 10-24 cm3/atom .s a release rate constant of approximately 10-3 s-1 and a trapping rate of the order of 1015 atoms, H/cm3 .s. TiC particles are irreversible traps with a large oc-cupancy and an interaction energy, .E(TiC-H), of 0.98 eV. The irreversible trapping parameters are calculated from the first permeation transient, where mixed trapping oc-curs. The trapping kinetics are about an order of magnitude faster than when only rever-sible trapping exists. The role of trapping on the effective diffusivity of hydrogen is dis-cussed as is, briefly, its role in affecting hydrogen-induced damage. Finally, guidelines are given to permit the trapping behavior of more general alloys to be analyzed.