Ahmed H. Backar

Temperature has a great influence on the mechanical properties of ductile cast iron or nodular cast iron. A thermomechanical treatment was carried out at various elevated temperatures of 450 °C, 750 °C and 850 °C using a universal testing machine with a tub furnace. Specimens were held at these temperatures for 20 min to ensure a homogeneous temperature distribution along the entire length of the specimen, before a tensile load was applied. Specimens were deformed to various levels of uniform strain (0%, 25%, 50%, 75%, and 100%). These degrees of deformation were measured with a dial gauge attached to a movable cross plate. Three strain rates were used for each specimen and temperature: 1.8×10−4 s−1, 9×10−4 s−1 and 4.5×10−3 s−1. A simple analytical model was extracted based on the CT tensile test geometry and yield stress and a 0.2% offset strain to measure the fracture toughness (JIC). To validate the analytical model, an extended finite element method (XFEM) was implemented for specimens tested at different temperatures, with a strain rate of 1.8×10−4 s−1. The model was then extended to include the tested specimens at other strain rates. The results show that increasing strain rates and temperature, especially at 850 °C, increased the ductility of the cast iron and thus its formability. The largest percentage strains were 1 and 1.5 at a temperature of 750 °C and a strain rate of 1.8×10−4 s−1 and 9×10−4 s−1, respectively, and reached their maximum value of 1.7 and 2.2% at 850 °C and a strain rate of 9×10−4 s−1 and 4.5×10−3 s−1, respectively. In addition, the simple and fast analytical model is useful in selecting materials for determining the fracture toughness (JIC) at various elevated temperatures and different strain rates.

A 6061 aluminum alloy has almost 0.8–1.2 wt.% Mg and 0.4–0.8 wt.% Si content. These two components, along with other alloying elements, therefore, were characterized by high mechanical and abrasive strength. The aims of the present work were to understand the effect of different types of cooling rates through different molds materials and to investigate the effect of casting with ceramic additives on segregation of the aluminum alloy itself as a composite material forum. Therefore, a series of mechanical tests were conducted, such as compression test, Vickers hardness, and pin-on-disc wear test. The samples were cast at 650 °C and in electric furnaces for 2 h to ensure that the metal achieved adequate homogeneity and temperature. Then, abrasive macroparticles of Al2O3 and Sic with a size close to 40–60 µm were used. The particles were poured under constant stirring for 1 min. Then, they were cast in two types of molds: steel and graphite. The cast specimens were obtained as a reference without particles and with 0.5 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, and 8 wt.%. The thermal effect and the heat due to conduction and radiation were calculated. The maximum compressive strength was found to increase by ≈21% with SiCp casted in graphite molds, and HV was found to increase by ≈29% with SiC casted in graphite molds. The same was found for wear resistance, which became good with SiC casted in graphite molds, and it was generally found that the cooling rate through the mold weakened the alloy due to the segregation effect. The presence of tough particulate through the aluminum matrix barrier created a number of loads. Additionally, the high specific heat of graphite, which plays a dominant role in the slaw cooling rate of casting, led to grain enlargement, whereas the higher cooling rate of steel led to grain refinement. These concepts are the main rules of heat treatments through the casting process itself, and they save time and effort.