Laser Surfacing Alloying of Nickel- and Iron-base Layer on A390 Aluminum

• Main Authors: Jia ChingYen, 嚴家慶
• Other Authors: Jong Ning Aoh
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/44662833614778840080

碩士 === 國立中正大學 === 機械系 === 92 === Laser surface alloying with Ni- and Fe-based powder on the surface of squeeze casing A390 aluminum alloy was conducted utilizing Nd-YAG laser. Powder deposition on the surface of A390 Al alloy prior to laser alloying was carried out by using plasma-spraying method. Through laser remelting of the surface coating and the base metal the mixture of the coating and substrate will form an alloyed layer with compounds. The laser alloyed coating exhibits improved wear and corrosion resistance. Relationship between laser processing parameters including laser power/scanning speed and the characteristics of Ni- and Fe-based alloyed layers on the surface of A390 Al alloy including hardness and geometrical features was investigated. Concentration of the beam energy by decreasing laser beam diameter would achieve completely molten surface. In general the hardened depth increased with increasing laser power and decreasing scanning speed. For multi-pass alloyed layer, the hardness decreases with increasing overlap between passes due to heat accumulation. A shallow hardened layer with hardness value higher than HV600 on the surface of A390 Al alloy can be achieved. Four different microstructures such as acicular structure, snow-flake structure, columnar dendrite and irregular lump existed in the single-pass Ni-based alloyed layer. The former three microstructures were formed to be Ni2Al3 intermetallic compound and the last was NiAl intermetallic compound identified by EDS and EPMA. However, acicular Ni2Al3 and irregular-shaped NiAl compounds mainly formed in multi-pass Ni-based alloyed layer, which was identified by XRD results. The NiAl compound is much harder than Ni2Al3 compound The microstructure of single-pass Fe-based alloyed layer mainly consisted of cellular dendrite and irregular lump, which were identified as Fe2Al5 and FeAl compounds respectively. Due to overlap and higher dilution, the upper and bottom of the multi-pass Fe-based alloyed layer consisted of Al-rich needle-like structure and Fe-rich irregular lump, which were identified as FeAl3 and FeAl compounds respectively by EDS and EPMA. XRD results also revealed that FeAl3 and FeAl compounds indeed existed in the multi-pass Fe-based alloyed layer. The adhesive wear of the Al substrate and the abrasive wear of Fe- and Ni-based alloyed layers was observed using SEM and OM. The wear loss of Ni-based alloyed layer was twice higher than that of Fe-based alloyed layer, indicating a superior wear resistance of Fe-based alloyed layer. Therefore, Fe-based alloyed layer could be applied in wear components to prolong the service life.