Improvement of Al-6061 alloys mechanical properties by controlling processing parameters
— this paper discusses the effect of casting processing parameter on the mechanical properties of Aluminum alloy 6061 companied with Al 2 O 3 and Si C P. The specimens were poured in two different mold types one of steel and the other of graphite. These two types have a wide range of cooling rate; steel has fast cooling rate whereas graphite has slow one. In order to investigate this effect, and the alloying elements participation the specimens were taken from three different positions in the mold; top, middle and bottom. The mechanical wear, hardness and microstructure examination were performed. The results showed that wear rate and hardness increase in case of specimen poured in steel mold. This increasing due to fast cooling rate which make refining of the grain size of aluminum alloys. Whereas, their mechanical properties decreased when using graphite molds. In contrast of this result, ductility is increased. This is attributed to that graphite has slow cooling rate (heat dissipate is low) which make enlargement to the grain size of aluminum alloy and the graphite is also solid lubricate playing as interactive lubricate which is main reason to decrease the wear rate.
Investigation of Heat Treatment on Al 6061- Al2O3 Composite & Analysis of Corrosion Behaviour
Al 6061-Al2O3 composite materials are world widely known because of their better strength and reduced weight. In this work three (6,9&15) weight percentage of Al 6061-Al2O3 composite materials were made through stir-casting process and their mechanical properties were studied. Another set of Al 6061-Al2O3 composite materials having weight percentage 6,9&15 were under gone mechanical property testing after solution heat treatment and made a comparison with non-heat treated one. Corrosion behaviour of both heat treated and non-heat treated were evaluated in NaOH, H2SO4 and NaCl solution by using weight loss method. Solution heat treatment helped the improvement in strength and corrosion resistance but the addition of volume percentage of alumina particle did not show a consistent trend. Keywords— Alumina particle, Corrosion, Solution heat-treatment, Stir-casting
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME