Unconventional Metallographic Methods for the Structural Characterization of Laser Hardened Al-Zn-Si Cast Alloy

Abstract:

The laser surface hardening is method which provides increased mechanical properties of secondary (recycled) Al-Si cast alloys for automotive industry. Improvement of mechanical properties and structure of secondary aluminium alloys can often significantly increase the lifetime of casting and reduce costs for fuel and reduction of environmental loading. For study was used a laser beam Nd: YAG lasers, BLS 720, on the test samples of secondary cast alloy AlZn10Si8Mg. AlZn10Si8Mg cast alloy are used for engine and vehicle constructions, hydraulic unit and mould making without the need of heat treatment because this alloy is self-hardened. The effect of laser beam was evaluated with the laser power 50 W and 80 W on the surface of samples. The final microstructure of Al-alloys depend on the laser process parameters. The changes of microstructure after laser surface hardening was observed by using classical techniques of etching (standard black-white contrast - etching by 0.5 % HF, 10 % H₃PO₄ and colour contrast - etching by Weck-Al) and deep etching with HCl. Due to the action of laser beam on the surface of the secondary alloy AlZn10Si8Mg there have been changes in the microstructure of the material. Melting area is alpha-phase with much fine columnar dendrites morphology without the presence of Si-particles and intermetallic phases. In the transition area were observed grain refinement of eutectic Si (finer and rounder Si particles) as the modify action of the laser. By increasing the laser power the microhardness of surface layers decreases. In the surface layer (80 W) were observed cracks due to uneven heat transfer of the material.

• Periodical: Materials Science Forum (Volume 782)
• Pages: 369-372
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.782.369
• Online since: April 2014
• Authors: Eva Tillová, Mária Chalupová
• Keywords: Aluminium Alloy, Colour Etching, Deep Etching, Laser Hardening, Scanning Electron Microscopy (SEM)

References

[1] Information on http: /world-aluminium. org.

[2] Information on www. rheinfelden-alloys. eu.

[3] R. C. P. Wong et al., Improvement of adhesive bonding using a laser surface texturing process. J. Mater. Proc. Technol. 63, (1997), 579-584.

[4] R. Li et al., Localised corrosion of laser surface melted 2024-T351 aluminium alloy. Surf. Coat. Technol. 81, (1996), 290-296.

DOI: 10.1016/0257-8972(95)02484-0

[5] K. G. Watkins et al., Influence of the overlapped area on the corrosion behaviour of laser treated aluminium alloys. Mater. Sci. Eng. A 252, (1998), 292-300.

DOI: 10.1016/s0921-5093(97)00695-3

[6] H. Geng, Y. Niu. et al., Laser surface strengthening process of Al-Si base alloy. Journal of Materials Sciences and Technology 17 (S1), (2001), 115-118.

[7] E. Tillová, E. Ďuriníková, M. Chalupová, Structural analysis of secondary AlZn10Si8Mg cast alloy. Acta Metallurgica Slovaca, Vol. 17, 1, (2011), 4-10.

DOI: 10.21062/ujep/x.2011/a/1213-2489/mt/11/1/11

[8] E. Tillová, E. Ďuriníková, M. Chalupová, Characterization of phases in secondary AlZn10Si8Mg cast alloy. Materials Engineering, Vol. 18, (2011), 1-7.

DOI: 10.21062/ujep/x.2011/a/1213-2489/mt/11/1/11

[9] E. Ďuriníková, E. Tillová, M. Chalupová, Phase and structure characteristics of recycled AlZn10Si8Mg cast alloy, Manufacturing Technology. Vol. 11, (2011), 11-17.

DOI: 10.21062/ujep/x.2011/a/1213-2489/mt/11/1/11