Study on Dissolution of Al2Cu in Al-4.3Cu and A205 Cast Alloys

Evolution of microstructure in a binary Al-Cu system (Al-4.3Cu) and a commercially alloyed Al-Cu system (A205) during solution heat treatment was investigated using optical microscopy (OM), scanning electron microscopy (SEM), wavelength-dispersive X-ray spectroscopy (WDS), and differential scanning calorimetry (DSC). The diversified coarseness of the microstructure was initiated by controlling the solidification rate. Different solution treatment temperatures were applied to identify a proper solutioning temperature. The larger microstructural scale required an increased solutioning temperature and prolonged holding time to obtain homogenized solutes in the α-Al matrix. The diffusion of Cu primarily controlled the solution heat treatment process. A diffusion-based model was applied and calibrated to determine the dissolution rate of an Al2Cu particle in the matrix. The model operates on a similar time scale with the experimental results for the Al-4.3Cu and A205 alloys with various microstructural scales, different chemical compositions, and at different solution treatment temperatures. Three-dimensional (3D) reconstructed images from SEM images and energy dispersive spectroscopy (EDS) map of elements showed that TiB2 particles shield the Cu-rich phases in the boundaries of α-Al grains, presumably acting as a physical barrier to the diffusion of Cu solutes toward α-Al grains. The model also suggests that the effective diffusion coefficient of Cu in Al, in the presence of TiB2 particles, reduced by a factor of 2.0–2.5 in the A205 alloy compared with the binary Al-Cu alloy.

Effects of Al Additions and Reheat Treatments on Microstructures of Modified Nickel-Based Superalloy, Grade Inconel 738, by Vacuum Arc Melting Process

This research has an aim to modify and improve the microstructures and hardness property of cast nickel-based superalloy, IN-738 by modified chemical composition of various Al additions as well as different reheat treatment conditions. IN-738 was modified by adding aluminium in 1, 2 and 3% by weight and casting with vacuum arc melting process. Then all casted alloys were performed with 5 different solutioning temperatures of 1125°C, 1145°C, 1165°C, 1185°C and 1205°C for 6 hours and all following with the same precipitation aging temperature of 845°C for 24 hours. The various obtained microstructures of the casting and reheat treatments were observed and investigated by SEM to evaluate the average area fraction and size of γ’ precipitated particles. The mechanical property was evaluated by Vickers hardness. From the obtained results, it was found that fine microstructure, which would be the most appropriate for using at elevated temperature, was obtained by the Al addition with 1%wt. following with solutioning temperature range between 1125°C – 1145°C/6 hours and precipitation aging at 845°C/24 hours. The microstructures received consist of high area fraction of γ’ particles in cubic shape with the proper size. However, the maximum hardness value of 683 HV was obtained from the alloy with 3%wt. Al addition following with solutioning temperature of 1205°C.