In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).

Laser Material Processing

Tool wear is a key issue for the friction stir welding (FSW) of aluminum matrix composites (AMCs), especially when the volume fraction of reinforcing particulates is relatively high. In this study, a threaded tool of WC–Co hard alloy is used to weld a cast AMC composed of Al–Si matrix and 30 vol%SiC particulates so as to examine the wear characteristics of the tool. Experimental results indicate that the tool wear is appreciable although the shoulder size and pin length are changed slightly. The radial wear of the pin is very different at different locations of the pin, and the maximum wear is finally produced at a location of about one-third pin length from the pin root. The welding speed has a decisive effect on radial wear rate of the pin, and the maximum wear rate is produced in the initial welding.

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Wear characteristics of a WC–Co tool in friction stir welding of AC4A+30 vol%SiCp composite

Microstructures and wear property of friction stir welded AZ91 Mg/SiC particle reinforced composite

A review about Friction Stir Welding of metal matrix composites

Co-based alloy coating was deposited on tool steel by powder feeding laser cladding. Sections of such coatings were examined to reveal their microstructures and phases using scanning electron microscope (SEM) and X-ray diffractometer (XRD). The results showed that the prime phase ( γ -Co dendrite) and other phases, including Cr 23 C 6 , Co 7 W 6 , and CrNi existed in the coatings. Some different solidification morphologies, such as planar (at the interface), cellular and dendrite formed, varying from the interface to the surface. Fine microstructures of γ -Co dendrite and lamellar eutectic in dendritical regions strengthened the coatings. Besides, the effects of aged treatment on the microstructure and microhardness of the surface coating were studied. Aged treatment led to the precipitations of some carbide particles (Cr 7 C 3 and Co 3 C) and boride particles (Co 4 B) from the cladded coating, causing an increase in microhardness in the laser-cladded coating.

Characteristics of cobalt-based alloy coating on tool steel prepared by powder feeding laser cladding

In this paper, ‘in-situ’ weld-alloying/laser beam welding with titanium as alloying element is utilized to join SiCp/6061Al MMC in order to prevent the formation of the needle-like harmful Al4C3 phases in the weld. Microstructure of the weld is characterized as functions of alloying content and processing parameters. Results show that the needle-like harmful aluminum carbides are completely eliminated. A central fusion weld joint reinforced by TiC, Ti5Si3 and Al3Ti is produced by ‘in-situ’ weld-alloying/laser beam welding of SiCp/6061Al MMC, while some large pores are formed in the partly melted zone.

L.G Yu

Papers

‘In-situ’ weld-alloying/laser beam welding of SiCp/6061Al MMC