Laser surface melting of Al–Co–rare earth (Ce–La) alloys for improving corrosion resistance

Abstract

The development of Al-RE (rare earth) alloys is primarily attributed to their excellent thermal stability, corrosion resistance, and tunable properties based on Co and Ce elements. Considering the need for a high critical cooling rate, it is a challenging phenomenon to develop fine and homogeneous Al-TM-RE alloy in bulk form. Therefore, it is a suitable alternative to use surface modification techniques to produce refined and homogenized coatings or thin films for achieving better corrosion resistance in the surface. In this study, the surface of two types of Al–Co–Ce–La alloys were treated by the Laser Surface Melting method with two different laser scanning speeds, and the effects of this process on the microstructure and corrosion properties were evaluated compared to the as-cast samples. The microstructural characteristics, chemical composition, phase change, and corrosion properties were evaluated. The results indicated that the particle sizes and the inter-particle distance in the Al matrix decrease significantly. The microstructure of the LSM samples are much more refined and homogenized, Compared to the as-cast crystalline material. The depth of microstructural affected zone by the laser surface process increased to an acceptable level (590 µm). No trace of microcrack formation and distortion were observed in the LSM samples. The decreased linear line energy from 83.6 to 41.8 j/mm led to the reduced interaction time and decreased amount of crystalline phases, thereby increasing the probability of amorphous structure. The best corrosion properties were obtained in the laser-treated Al83.0Co10.0-Ce4.3-La2.7 alloy with a scanning speed of 20 mm/s.