Homogenization of the element distribution during wire electron beam cladding of CuAl8 onto AlSi10Mg

Hengst Philipp - TU Bergakademie Freiberg (Germany)

Hard coatings provide excellent properties in terms of wear and corrosion protection. However, on soft substrates such as aluminum alloys, there is insufficient support for such coatings, necessitating an additional surface treatment. By surface remelting and alloying or cladding, the wear resistance, corrosion protection, and support for hard coatings can be improved in aluminum alloys. In particular, cladding (one-step process) offers the advantage over surface remelting and alloying (two-step process) because pre-deposition of alloying elements is not required and it is characterized by high productivity.

A key factor for the success of surface alloying is the uniform distribution of the alloying elements. Particularly in wire-based cladding, there is still a need for research to obtain a homogeneous element distribution in the deposited layers. The goal of this work was to generate crack-free cladded layers with the highest possible hardness on aluminum alloys, providing sufficient support for subsequent hard coatings. The focus was initially placed on homogenizing the element distribution in wire-based cladding using the capabilities of electron beam technologies.

A CuAl8 wire was applied to an aluminum alloy AlSi10Mg using both front and back wire feeding techniques. The oscillation patterns used for the electron beam were the concentric circles pattern and a Medusa-shaped pattern, which primarily differ in terms of energy distribution. In addition to the deposition geometry, the distribution of alloying elements was characterized using backscattered electron images and additional energy-dispersive X-ray mappings. Finally, hardness mappings were conducted.

It was shown that the oscillation patterns significantly influence the width and penetration depth of the deposited layers due to the different energy distributions. Compared to the front feeding cladding, the samples with back feeding exhibited deeper penetration. The cladded beads with back feeding showed a very inhomogeneous distribution of alloying elements and contained numerous small Cu-rich microstructural components. In contrast, front feeding resulted in a more homogeneous Cu distribution. The hardness mappings confirmed these findings, showing a narrower hardness distribution for the front-fed deposits compared to the back-fed deposits.

Thus, the choice of oscillation pattern combined with the wire feeding technique can significantly influence the distribution of alloying elements. Based on the current state of research, front feeding is always preferred over back feeding cladding. These results form the foundation for further studies aimed at generating crack-free cladded layers with the highest possible hardness to provide good support for hard coatings.

Keywords:

surface engineering, electron beam, wire, cladding, element distribution