Effects of CNTs on microstructure and hardness of laser welds of the CNT-reinforced magnesium composite

• Published in: Composites. Part A, Applied science and manufacturing Vol. 48; pp. 67 - 72
• Main Authors: Qian, M., Goh, C.S., Sun, Y.H., Ng, F.L.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.05.2013; Elsevier
• Subjects: A. Nano-structures; annealing; Applied sciences; B. Hardness; B. Microstructures; Carbon; carbon dioxide; carbon nanotubes; dendrites; Dendritic structure; Dispersion hardening metals; Exact sciences and technology; hardness; Irradiation; Laser beam welding; Laser welding; Magnesium; Metals. Metallurgy; Microstructure; particles; Particulate composites; Powder metallurgy. Composite materials; Production techniques; solidification; Welded joints; A. Nano-structures; B. Hardness; B. Microstructures; Laser welding; Annealing; Metal matrix composite; Carbon nanotubes; Mechanical properties; Experimental study; Microhardness; Composite material; Dispersion strengthened metal; Multiwalled nanotube; Nanocomposite; Microstructure
• ISSN: 1359-835X; 1878-5840
• DOI: 10.1016/j.compositesa.2013.01.013

A magnesium composite reinforced with 1.3wt.% multiwall carbon nanotubes (MWCNTs) was welded using a CO2 laser. Abundant nanoscale and submicron carbon particles formed in the laser welds, owing to the coalescence of the reinforcing CNTs as the result of conjoint effect of laser irradiation and welding thermal annealing. Dense intra- and inter-granular carbon particles and carbon particle-enveloped equiaxed dendrites in the magnesium matrix constituted the characteristic weld microstructure. Lateral-irregular cellular growth originated from the weld fusion boundary and the carbon particle-enveloped equiaxed dendrites with substructure formed in the weld center. It is inferred that the CNTs affected the weld solidification mainly via retarding solidification growth rate. The gained weld hardening is primarily attributed to the local refined weld microstructure and locally denser carbon particles and MWCNTs. Lower laser fluence facilitated finer weld structure and less laser irradiation on the CNTs hence more hardening effect.