Alloy Design for Semi Solid Metal Forming

Abstract:

Semi-solid metal forming is more than 40 years old but its full potential to near net shape form high strength aluminium alloys has been realised only to a limited degree. Alloys developed for traditional manufacturing processes were initially used but it became apparent that alloys specific to SSM forming needed to be developed. The main alloy development criteria revolved around SSM processing temperature, solid fraction (f_s) versus temperature sensitivity and age hardening potential. This methodology while sound does not fully address the unique processing behaviour of SSM forming. By its very nature SSM requires the controlled solidification of a part of the melt before forming. From basic solidification fundamentals this results in the enrichment of the remaining liquid with alloying elements. During the forming process segregation of liquid phase essentially produces a component with very different compositions in the regions where the liquid solidifies last. From recent work completed on a wide range of standard alloy systems it has become apparent that this segregation effect has a significant impact on aging behaviour and strength. Low melting point structures formed in the these regions result in localised melting in the grain boundary region and along areas of gross liquid segregation during solution heat treatment, contributing to the poor mechanical properties. Although this behaviour can be addressed using modified heat treatment, this cannot be applied to all current alloy systems. Alloy design for SSM forming must take these phenomena into account in order to develop and or specify aluminium alloys with acceptable mechanical properties.

• Periodical: Materials Science Forum (Volumes 783-786)
• Pages: 136-141
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.783-786.136
• Online since: May 2014
• Authors: Gonasagren Govender*, Heinrich Möller, Ulyate Andries Curle
• Keywords: Al-Cu-Mg, Al-Mg-Si, Al-Zn-Mg-Cu Aluminium Alloys, Rheo-High Pressure Die Casting (R-HPDC)

References

[1] D. B Spencer, R. Mehrabian and M.C. Flemings, Rheological Behavior of Sn 15 Pct Pb in the Crystallization Range, Metallurgical Transactions (3) (1972) 1925 – (1932).

DOI: 10.1007/bf02642580

[2] Z. Fan, Semisolid metal processing. " International Materials Reviews (47. 2) (2002) 49-85.

[3] H.V. Atkinson, Alloys for Semi-Solid Processing, Solid State Phenomena, Vols. 192-193, 2013, pp.16-27.

DOI: 10.4028/www.scientific.net/ssp.192-193.16

[4] S. Chayong, H.V. Atkinson and P. Kapranos, Thixoforming 7075 aluminium alloys, Materials Science and Engineering A, 390, 2005, pp.3-12.

DOI: 10.1016/j.msea.2004.05.004

[5] A.M. Camacho, H.V. Atkinson, P. Kapranos and B.B. Argent, Thermodynamic predictions of wrought alloy compositions amenable to semi-solid processing, Acta Materialia, 51, 2003, pp.2319-2330.

DOI: 10.1016/s1359-6454(03)00040-5

[6] U.A. Curle, H. Möller and G. Govender, R-HPDC in South Africa, Solid State Phenomena, Vols. 192-193, 2013, pp.3-15.

DOI: 10.4028/www.scientific.net/ssp.192-193.3

[7] G. Vaneetveld, A. Rassili, J-C. Pierret and L. Lecomte-Beckers, Improvement in Thixoforging of 7075 Aluminium Alloys at High Solid Fraction, Solid State Phenomena, Vols. 141-143, 2008, pp.707-712.

DOI: 10.4028/www.scientific.net/ssp.141-143.707

[8] J.B. Patel, Y.Q. Liu, G. Shao and Z. Fan, Rheo-processing of an alloy specifically designed for semi-solid metal processing based on the Al-Mg-Si system, Materials Science and Engineering A, 476, 2008, pp.341-349.

DOI: 10.1016/j.msea.2007.05.046

[9] M.S. Salleh, M.Z. Omar, J. Syarif and M.N. Mohammed, Thermodynamic Calculations of Aluminium Alloys for Semi-Solid Processing", Recent Advances in Mathematics In Proceedings of the 7th Int. Conf. on Applied mathematics, Simulation, Modelling (ASM, 13), pp.266-270.

[10] R Sauermann, A. Arnold, B. Friedrich, B. Hallstedt and J.M. Schneider, Development of Al-Li based Alloys for thixoformed Automotive Parts, In Proceedings of EMC, (2005).

[11] U.A. Curle, H Möller and J.D. Wilkins, Shape rheocasting of high purity aluminium, Scripta Materialia, 64, 2011, pp.479-482.

DOI: 10.1016/j.scriptamat.2010.11.010

[12] U.A. Curle, H Möller and J.D. Wilkins, Shape rheocasting of Al-Si binary eutectic, Materials Letters, 65, 2011, pp.1469-1472.

DOI: 10.1016/j.matlet.2011.02.040

[13] G. Govender and H. Möller, Evaluation of Surface Chemical Segregation of Semi-Solid Cast Aluminium Alloy A356, Solid State Phenomena, Vols. 141-143, 2008, pp.433-438.

DOI: 10.4028/www.scientific.net/ssp.141-143.433

[14] H. Möller, U.A. Curle and E.P. Masuku, Characterization of surface liquid segregation in SSM-HPDC aluminium alloys 7075, 2024, 6082 and A201, Trans. Nonferrous Met. Soc. China, 20, 2010, pp.847-851.

DOI: 10.1016/s1003-6326(10)60593-6

[15] L. Chauke, H. Möller, U.A. Curle and G. Govender, Anodising of Al-Mg-Si-(Cu) alloys produced by R-HPDC, Proceedings of LMT 2013 conference Materials Science Forum, Vol. 765, 2013, pp.658-662.

DOI: 10.4028/www.scientific.net/msf.765.658