PRODUCTION OF CAST AZ91-CNT NANO-COMPOSITE BY ADDITION OF Ni-P-CNT COATED MAGNEIUSM POWDER TO THE MELT

摘要

High agglomeration tendency and poor wettability of CNTs with metallic matrices are the main challenges for using this unique material as the reinforcement in magnesium based composites. In this study, nickel- phosphorous electroless coating process was employed for uniform co-deposition of CNTs into the Ni-P coating on the magnesium powder for the first time. The magnesium powder with the optimum composite coating was then used as the reinforcement and was introduced into the molten AZ91 alloy using stir casting method. Similar composites were also produced with untreated as-purchased CNTs for comparison. It was observed that addition of CNTs dispersed in the electroless coating resulted in refinement of the grain size, reduction in the porosity content and improvement of the hardness and flexural strength. Untreated CNTs were not able to improve the structural and mechanical characteristics of the cast composites to the same extent. This is believed to be due to the more agglomeration, less uniform distribution and poor wettability of the untreated CNTs with the melt compared to those introduced to the melt through the Mg-Ni-P-CNT composite powder.