**Andrea Francesco Ciuffini 1,\*, Silvia Barella 1, Cosmo Di Cecca 1, Andrea Gruttadauria 1, Carlo Mapelli 1, Luca Merello 1, Giacomo Mainetti <sup>2</sup> and Massimo Bertoletti <sup>2</sup>**


Received: 5 May 2018; Accepted: 29 May 2018; Published: 1 June 2018

**Abstract:** 6xxx aluminum alloys are suitable for the realization of both structural applications and architectural decorative elements, thanks to the combination of high corrosion resistance and good surface finish. In areas where the aesthetic aspects are fundamental, further improvements in surface quality are significant. The cooling of the extrusion mold via internal liquid nitrogen fluxes is emerging as an important innovation in aluminum extrusion. Nowadays, this innovation is providing a large-scale solution to obtain high quality surface finishes in extruded aluminum semi-finished products. These results are also coupled to a significant increase in productivity. The aim of the work is to compare the surface quality of both cooled liquid nitrogen molds and classically extruded products. In this work, adhesion phenomena, occurring during the extrusion between the mold and the flowing material, have been detected as the main causes of the presence of surface defects. The analysis also highlighted a strong increase in the surface quality whenever the extrusion mold was cooled with liquid nitrogen fluxes. This improvement has further been confirmed by an analysis performed on the finished products, after painting and chromium plating. This work on the AA6060 alloy has moreover proceeded to roughness measurements and metallographic analyses, to investigate the eventual occurrence of other possible benefits stemming from this new extrusion mold cooling technology.

**Keywords:** aluminum; extrusion; liquid nitrogen cooling; surface quality; aesthetic
