Effects of Heat Treatment on the Microstructure and Hardness of A356 (AlSi7Mg0.3) Manufactured by Vertical Centrifugal Casting

The A356 alloy has been widely used in automotive components, such as wheels and brake disks, because it is an excellent lightweight material with high corrosion resistance and good mechanical properties. Recently, to reduce the weight of brake disks, the Fe-A356 hybrid brake disk has been suggested. Because brake disk quality is directly related to driving safety, the T4/T6 heat treatment of centrifugally cast A356 alloys were performed to enhance the mechanical properties and reduce micro-segregation. The solid-solution heat treatment followed by annealing caused the formation of Mg-rich intermetallic compounds on the grain boundaries of the Al matrix, decreasing the average hardness of the alloys by 13 HV. In contrast, the solid solution followed by water quenching (T4) reduced the area fractions of the intermetallic compounds and increased the average hardness by 11 HV. The T6 heat-treated A356 alloys, which were influenced by the formation of the Guinier–Preston zone exhibited a relatively higher average hardness, by 18 HV, compared to T4 heat-treated A356 alloys.

FEM Simulation of Waves Excited by Array Probe Propagating in Centrifugally Cast Stainless Steel With Hexagonal Column

Centrifugally cast stainless steel (CCSS) is widely used in PWR primary coolant systems. However, ultrasonic testing for such material is very challenging because its coarse grains and anisotropic property. The phased array ultrasonic technology (PAUT) is considered the most promising solution to the problem mentioned. To improve the accuracy of PAUT for CCSS with columnar grains, we used the voxel-based finite element method to perform simulation of wave propagation in CCSS, where waves were excited by a linear array. We modeled columnar grains in CCSS with hexagonal columns and introduced a side-drilled hole. It was easily to have different inclined columnar grains by rotating the crystal axes. All column crystals were considered cubic crystals while CCSS with columnar grains was macroscopically transversely isotropic. Wave propagations were computed for different focal laws and their results were compared. Waves exactly propagated toward and focused at the targeted SDH when focal laws were calculated according to the anisotropic property of CCSS, but deviated the target for focal laws based on isotropy.

Centrifugally-cast concrete poles with non-metallic reinforcement

The article describes the testing of poles for electric power transmission lines, which are made of centrifugally-cast concrete and ultra-high strength concrete, and which are prestressed with Carbon Fibre Reinforced Polymer tendons (CFRP). The presented results of pole ultimate load testing suggest the potential for usage of this construction product, particularly in aggressive environments with high probability of steel corrosion. Part of the tested poles had shear reinforcement in the form of confined Glass Fibre Reinforced Polymer (GFRP) grid, while one share of samples had no shear reinforcement, but the concrete matrix was strengthened with synthetic macro fibres. A review is given on similar product testing, calculation methods, and guidance is provided for further research.

Through-Thickness Microstructure Characterization in a Centrifugally Cast Austenitic Stainless Steel Nuclear Reactor Primary Loop Pipe Using Time-of-Flight Neutron Diffraction

The US code of Federal Regulations mandates regular inspection of centrifugally cast austenitic stainless steel pipe, commonly used in primary cooling loops in light-water nuclear power plants. These pipes typically have a wall thickness of ~8 cm. Unfortunately, inspection using conventional ultrasonic techniques is not reliable as the microstructure strongly attenuates ultrasonic waves. Work is ongoing to simulate the behavior of acoustic waves in this microstructure and ultimately develop an acoustic inspection method for reactor inspections. In order to account for elastic anisotropy in the material, the texture in the steel was measured as a function of radial distance though the pipe wall. Experiments were conducted on two 10 × 12.7 × 80 mm radial sections of a cast pipe using neutron diffraction scans of 2 mm slices using the HIPPO time-of-flight neutron diffractometer at the Los Alamos Neutron Science Center (LANSCE, Los Alamos, NM, USA). Strong textures dominated by a small number of austenite grains with their (100) direction aligned in the radial direction of the pipe were observed. ODF analysis indicated that up to 70% of the probed volume was occupied by just three single-grain orientations, consistent with grain sizes of almost 1 cm. Texture and phase fraction of both ferrite and austenite phases were measured along the length of the samples. These results will inform the development of a more robust diagnostic tool for regular inspection of this material.