Neutron Diffraction Analysis of Residual Strain in High-Pressure Die Cast A383 Engine Blocks
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JMEPEG https://doi.org/10.1007/s11665-020-05019-x
Neutron Diffraction Analysis of Residual Strain in High-Pressure Die Cast A383 Engine Blocks Tao Liu, Jeffrey R. Bunn, Chris M. Fancher, Laurentiu Nastac, Vish Arvikar, Ilya Levin, and Luke N. Brewer (Submitted February 24, 2020; in revised form May 4, 2020) The residual strains in three high-pressure die cast A383 engine blocks were measured using neutron diffraction. Residual strains and stresses can be generated during high-pressure die casting process due to high thermal gradients and may cause fatigue failure or dimensional distortion. Neutron diffraction can measure the residual strain distributions deep inside castings with complex geometries, because neutrons can penetrate substantially more material than x-rays. In the present work, the residual strains (in the axial and hoop directions) along the whole cylinder bridge of high-pressure die cast A383 engine blocks in as-cast and heat-treated conditions were measured by neutron diffraction methods. The effect of heat treatment on the distribution and magnitude of residual strains was also investigated. The results indicate that the residual strain in the cylinder bridge is tensile in both the axial and hoop components for both the as-cast and the heat-treated engine blocks. The residual strain in the hoop direction is bigger in magnitude than the residual strain in the axial direction. Heat treatment significantly relaxes the residual strain in the axial direction but only slightly relaxes the residual strain in the hoop direction. Keywords
aluminum alloy, high-pressure die casting, neutron diffraction, residual stress
1. Introduction Aluminum (Al) alloys possess low density ( 2.7 g/cm3) and are widely used to manufacture automotive components in order to improve the fuel efficiency of vehicles (Ref 1). Highpressure die casting has extremely high cooling rates during solidification (up to 100 K/s) and is a cost-effective technique for manufacturing of aluminum alloy engine blocks (Ref 2). Due to the relatively low wear resistance of aluminum, protective cylinder liners, made of gray cast iron, are commonly used within the combustion chambers (Ref 3). Large residual stresses may be generated in the cylinder bridge region from two factors: (1) thermal gradients during the cooling process (after casting or heat treatment) and (2) large difference in the thermal expansion coefficient of the gray cast iron and the adjoining Al alloys (aAl = 2.1 9 105K1, aFe = 1.05 9 105K1) (Ref 4). Permanent dimensional distortion or fatigue failure may be caused by the large residual stresses in the engine blocks (Ref 5-7); therefore, measurement and control of the residual stresses level in the engine blocks are of vital importance. Many techniques are available to measure the residual stresses in engine blocks. A destructive method operated by
Tao Liu, Laurentiu Nastac, and Luke N. Brewer, Department of Metallurgical and Materials Engineering, The University of Alabama, Box 870202, Tuscaloosa, AL 35487; Jeffrey R. Bunn and
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