New Copper Alloy Powder for Laser-Clad Valve Seat Used in Aluminum Cylinder Heads

A copper alloy powder composed of Cu-14Ni-3Si-2V-2Cr-1.5Fe-1Al-0.5P has been developed for application to laser-clad valve seats. Laser-clad valve seats offer several advantages such as higher engine output and improved fuel economy owing to lower valve head temperature and an increased intake throat diameter compared with conventional press-fit valve inserts made of ferro-based powder metal.

Previously, a material having a principal chemical composition of Cu-12Ni-10Co-3Si-2V-2Nb-1.5Fe-1Al was developed to obtain large hard intermetallic compounds. The microstructure of this material is formed by a two-liquid separation reaction, which has been applied to powders of different chemical compositions for laser-clad valve seats of production engines. Although this material shows superior valve seat wear resistance, it has certain drawbacks, including the high cost of the powder, high probability of microcrack formation and low machinability of the laser-clad layer.

The key issue in designing the new material was to obtain a microstructure dispersed with fine compounds. This has been accomplished by changing the reaction from the two-liquid separation type to the monotectic type as a result of omitting cobalt and niobium and adding phosphorus. The chemical composition of the powder was determined by narrowing down the candidate materials on the basis of high-temperature hardness and the quantity of intermetallic compounds formed. That was done through tests conducted with ingots, followed by valve/valve seat rig tests using the laser-clad cylindrical samples and finally engine tests using a cylinder head with laser-clad valve seats. Machinability tests were also performed on cylinder heads fitted with laser-clad valve seats. The new alloy resolves the drawbacks of the previous material and is expected to contribute to expanded use of laser-clad valve seat technology in new engines in the future.