Influence of tin and bismuth on machinability of lead free 6000 series aluminium alloys

Abstract

The present paper presents the microstructural characteristics of an extruded AA6012A-T6 (AlMgSiBiSn) alloy and the microstructural changes occurring during turning operations, analysing the mechanism involved in chip breaking. An experimental investigation has been conducted to determine the effects of different cutting speed and feedrate on the machinability of the alloy. The machinability of the AA6012A-T6 alloy, where Pb is substituted by Bi and Sn, has then been compared to the standard AA6012-T6 (AlMgSiPb) and AA6082-T6 (AlSiMg) alloys. The results indicate that the extensive plastic deformation induces a preferred orientation of the grain structure and secondary phases along the shear plane, and a local increase in the alloy temperature. Low melting point compounds, such as the Sn and Bi bearing particles, transform into a soft or liquid state, changing their initial compact shape to assume a needle-like morphology. The β-Mg₂Si and α-Al(FeMn)Si particles are not influenced by the working temperature and keep their initial shape. The AA6082-T6 alloy shows a very poor machinability, with long and continuous strips, while the AA6012A-T6 alloy reveals a good chip formation with small and discontinuous C shaped chips, similar to the AA6012-T6 (AlMgSiPb) alloy. In particular, a feedrate higher than 0·2 mm rev⁻¹ provides short and suitable chips, independently of cutting speed.

Keywords

Aluminium alloys Microstructure AA6012A Sn Bi Machinability

Get full access to this article

View all access options for this article.

References

Kalpakjian

and Schmid

S. R.

: ‘Manufacturing processes for engineering materials’, 4th edn, 416–514; 2003, Upper Saddle River, NJ, Pearson Education Inc.

Astakhov

V. P.

, Shevets

S. V.

and Osman

M. O. M.

: J. Mater. Process. Technol. , 1997, 71, 247–257.

Grum

and Kisin

: Int. J. Mach. Tools Manuf. , 2003, 43, 1535–1543.

Grum

and Kisin

: Int. J. Mach. Tools Manuf. , 2003, 43, 1545–1551.

Sadik

M. I.

and Lindström

B. O.

: J. Mater. Process. Technol. , 1995, 54, 12–16.

Shinozuka

, Obikawa

and Shirakashi

: J. Mater. Process. Technol. , 1996, 62, 345–351.

Muhsin

I. S.

: ‘The role of the contact length as a governing factor in cutting process’, PhD thesis, Royal Institute of Technology, Stockholm, Sweden, 1991.

in ‘ASM Handbook’, Vol. 16, ‘Machining of aluminum and aluminum alloys’, (ed. Davis

J. R.

), 761–804; 1989, Materials Park, OH, ASM International.

Bray

J. W.

: in ‘Aluminum mill and engineered wrought products’ (ed. Rooy

E.L.

), Vol. 2, 17–483; 1989, Materials Park, OH, ASM International.

10.

Wouters

and de Hosson

J. Th. M.

: Mater. Sci. Eng A , 2003, A361, 331–337.

11.

Sircar

: ‘Free machining aluminum alloy containing bismuth or bismuth-tin for free machining and a method of use’, US patent no. 6409966, Reynolds Metals Company, Richmond, VA, USA, 2002.

12.

Sircar

: ‘Free-machining aluminum alloy and method of use’, US patent no. 6315947, Reynolds Metals Company, Richmond, VA, USA, 2001.

13.

Bartges

C. W.

and Klemp

T. J.

: ‘Lead-free 6XXX aluminium alloy’, European patent no. 1464717, Alcoa Center, PA, USA, 2004.

14.

Farrar

L. E.

and Coats

N. L.

: ‘Lead-free 6000 series aluminum alloy’, US patent no. 5810952, Kaiser Aluminum and Chemical Corporation, Oakland, CA, USA, 1998.

15.

Røyset

, Sæter

J. A.

, Ustad

and Reiso

: Mater. Sci. Forum , 2002, 396–402, 1205–1210.

16.

Koch

and Antrekowitsch

: BHM , 2008, 153, 278–281.

17.

Timelli

, Faresin

, Bonollo

, Fantinel

and de Cet

: Proc. 32th AIM National Conf., Ferrara, Italy, September 2008, University of Ferrara, Paper 126.

18.

Vander

G. F.

Voort: ‘Metallography: Principles and practise’, 1st edn, 511; 1984, New York, McGraw-Hill.

19.

‘Tool-life testing with single-point turning tools’, Standard 3685, ISO Geneva, Switzerland, 1993.

20.

Reiso

: ‘Extrusion of AlMgSi alloys’, Mater. Forum , 2004, 28, 32–46.

21.

Jaspers

: ‘Metal cutting mechanics and material behaviour’, PhD thesis, Eindhoven: Tecnishe Universiteit Eindhoven, Eindhoven, the Netherlands, 1999.

22.

de Haas

Marc-Jan

: ‘Grain boundary phenomena and failure of aluminium alloys’, PhD thesis, University of Groningen, Groningen, the Netherlands, 2002.

23.

Shaw

M. C.

: ‘Metal cutting principles’, 2nd edn; 1984, New York, Oxford University Press.

24.

Agarwal

, Gokhale

A. M.

, Graham

and Horstemeyer

M. F.

: Mater. Sci. Eng A , 2003, A331–A337, 35–42.

25.

Balasundaram

, Gokhale

A. M.

, Graham

and Horstemeyer

M. F.

: Mater. Sci. Eng A , 2003, A355, 368–383.

26.

Xie

: ‘Mechanics of metal cutting through a solid mechanics approach; adiabatic shear banding’, PhD thesis, Washington State University, Washington, USA, 1995.