Investigations on Pb-free 6000 series aluminum alloy for machining applications

Pb-based alloys such as AA6262, AA2011 and more recently AA6026 are used as free-machining aluminum alloys for automotive and electronic applications. However, in order to comply with Automotive End of Life Vehicles (ELV) and Restriction of Hazardous Substances (RoHS) directives, Pb-based alloys slowly need to be phased out. A Pb-free machining grade 6xxx aluminum alloy based on Sn was developed and its machinability evaluated. Microstructure analysis of the Al–Mg–Si–Sn–Cu alloy revealed the presence of (98 wt%) Sn–Mg2Sn eutectic phases, which have a low melting point of ~203 °C, and are responsible for providing good machinability. Homogenized billets of the alloy were extruded and heat treated to T6 temper. Yield strength and ultimate tensile strength of the Pb-free alloy were comparable to those of the conventionally used Pb-based AA6262-T6 alloy. Machinability studies of the alloy were conducted by evaluating the effect of cutting speed, feed rate and depth of cut on surface roughness, chip size and form of chip produced during the turning operation. The machinability of the Sn containing alloy was found to be superior to that of non-machining grade 6xxx alloys AA6061-T6 and AA6082-T6 and comparable to that of Pb-based free-machining alloy AA6262-T6.