Failures Related to Castings

The information provided in this article is intended for those individuals who want to determine why a casting component failed to perform its intended purpose. It is also intended to provide insights for potential casting applications so that the likelihood of failure to perform the intended function is decreased. The article addresses factors that may cause failures in castings for each metal type, starting with gray iron and progressing to ductile iron, steel, aluminum, and copper-base alloys. It describes the general root causes of failure attributed to the casting material, production method, and/or design. The article also addresses conditions related to the casting process but not specific to any metal group, including misruns, pour shorts, broken cores, and foundry expertise. The discussion in each casting metal group includes factors concerning defects that can occur specific to the metal group and progress from melting to solidification, casting processing, and finally how the removal of the mold material can affect performance.

A Study Of Cylinder Bore Distortion In V6 Aluminum Alloy Engine Blocks

This study investigates the potential factors which may cause cylinder bore distortion in V6 aluminum engine block with cast-in gray iron liners. In this research, the microstructure, mechanical properties and residual stress of 319 type aluminum alloy engine blocks were analyzed from top to bottom along the interbore regions in the TSR, T7 heat treated and service (dyno) tested conditions. The results suggest that the cooling rate increased significantly along the cylinder in the vicinity of the chill plate at the bottom of the engine block. This caused a significant refinement in the microstructure which increased the hardness and tensile strength at the bottom of the cylinder relative to the top. The increased strength at the bottom of the cylinder prevented the rapid relief of residual stress at elevated temperature, which suggests that the bottom of the cylinder is less susceptible to cylinder distortion.

A Study Of Cylinder Bore Distortion In V6 Aluminum Alloy Engine Blocks

This study investigates the potential factors which may cause cylinder bore distortion in V6 aluminum engine block with cast-in gray iron liners. In this research, the microstructure, mechanical properties and residual stress of 319 type aluminum alloy engine blocks were analyzed from top to bottom along the interbore regions in the TSR, T7 heat treated and service (dyno) tested conditions. The results suggest that the cooling rate increased significantly along the cylinder in the vicinity of the chill plate at the bottom of the engine block. This caused a significant refinement in the microstructure which increased the hardness and tensile strength at the bottom of the cylinder relative to the top. The increased strength at the bottom of the cylinder prevented the rapid relief of residual stress at elevated temperature, which suggests that the bottom of the cylinder is less susceptible to cylinder distortion.

Graphite Dendrites in Cast Iron and Their Fundamental Role in the Control of Morphology to Obtain Aero-Eutectic Graphite

This work analyzes the growth of graphite in the eutectic system of gray cast iron, focusing on laminar type A and undercooled type D morphology, and a modified morphology, such as vermicular or compact graphite. The objective of the study is to find an optimal graphite structure, from which a new class of lightweight materials results that has been called aero-eutectic graphite (AEG). The method to obtain AEG consists of dissolving the gray iron ferrous matrix by means of a chemical attack. From experiences of unidirectional solidification, it has been found that laminar graphite grows in a non-faceted way, coupled to austenite, while in vermicular the growth is through foliated dendrites. This characteristic allows vermicular graphite to have a higher specific intrinsic surface area. According to the Brunauer-Emmett-Teller (BET) analysis, the surface of the vermicular was 106.27 m2 g−1, while those corresponding to type A and D were 83.390 m2 g−1 and 89.670 m2 g−1, respectively. AEG with graphite type D was used as a cathode in Li-O2 batteries with satisfactory results, reaching more than 70 charge and discharge cycles, and 150 cycles at this time and still cycling, using Ru(bpy)3(ClO4)2 as redox mediator.

Metallurgical and Mechanical Failure Analysis of an Aftermarket Flywheel

A failure analysis investigation was performed on the remnants of an aftermarket gray cast iron flywheel that catastrophically fractured during operation in a vehicle after 24 miles of operation. Light microscopy, 3D X-ray micro-computed tomography (micro-CT), scanning electron microscopy (SEM), metallography, and hardness/tensile testing techniques were utilized to characterize manufacturing quality, mode(s) of failure, microstructural variation, fracture surfaces, and mechanical properties of the failed component. Light microscopy examination of the remnant surfaces showed that the flywheel shattered with signs of radial heat checking fissure cracks. A metallurgical examination of the flywheel showed that it was manufactured from cast gray iron, with evidence of microstructural changes near heat-affected zones from graphite flakes in a ferrite/pearlite matrix to needle and lath formations similar to bainite or martensitic phases. The CT scan slices and fracture surface examination in the SEM showed signs of porosity and dendritic formations along a fracture surface believed to be the crack initiation location. The analysis suggests manufacturing flaws found within the flywheel were a likely contributing factor leading to premature failure during service.