Laser alloying: A tool to produce improved Al-Mo surface alloys Available to Purchase

The production of Al-transition metal alloys by laser alloying requires the treatment to be carried out at low scanning speeds in order to dissolve the high melting point addition elements. This procedure results in alloys containing a significant number of defects and large primary intermetallic compound particles that reduce the treatment’s usefulness. To overcome this problem a two-step laser processing technique was developed, consisting of a preparatory step, using long interaction times, followed by a structure-refinement step, using short interaction times. This concept was tested in the production of Al-(3.5-8.6 wt.%)Mo surface alloys with improved strength. The alloys were prepared by alloying Mo powder into Al using a CO₂ laser and an interaction time τ=0.26 s. Their structure is formed of coarse needle-shaped and equiaxed (cubic, rectangular, etc.) particles of Al₅Mo intermetallic compound dispersed in a cellular-dendritic matrix of α-Al. Remelting was performed using 0.03<τ<0.26 s. In the remelted layers the same intermetallic compounds were found, but most particles are composite and present a radial morphology. Growth of these particles often occurred on primary equiaxed or needle-like particles that did not dissolve during remelting. The volume fraction of intermetallic compounds increases with the remelting speed, resulting in surface layers with increasing hardnesses, up to 350 HV.