Abstract: Al-Si-Mg-Ni(-Cu) alloys are widely used in the automotive industry. They have the advantage of low weight associated with low coefficient of thermal expansion and excellent mechanical properties – mainly at high temperatures. The corrosion resistance of these alloys in coastal area, particularly sea water, however is not yet known. In this investigation, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization have been used to evaluate the corrosion resistance of Al-6Si-0.5Mg-2Ni (-2Cu) alloys in simulated sea water environments. The potentiodynamic polarization curves reveal that 2 wt% Cu content alloy (Alloy-2) is more prone to corrosion than the Cu free alloy (Alloy-1). But the EIS test results showed that corrosion resistance or charge transfer resistance (Rct) increases with the addition of Cu. Due to addition of Cu and thermal treatment, the magnitude of open circuit potential (OCP), corrosion potential (Ecorr) and pitting corrosion potential (Epit) of Al-6Si-0.5Mg-2Ni alloy in NaCl solution were shifted to the more noble direction.
Abstract: Effect of 2wt% Cu addition on tensile properties and
fracture behavior of Al-6Si-0.5Mg-2Ni alloy at various strain rates
were studied. The solution treated Al-6Si-0.5Mg-2Ni (-2Cu) alloys,
were aged isochronally for 1 hour at temperatures up to 300oC. The
uniaxial tension test was carried out at strain rate ranging from 10-4s-1
to 10-2s-1 in order to investigate the strain rate dependence of tensile
properties. Tensile strengths were found to increase with ageing
temperature and the maximum being attained ageing for 1 hr at
225oC (peak aged condition). Addition of 2wt% Cu resulted in an
increase in tensile properties at all strain rates. Evaluation of tensile
properties at three different strain rates (10-4, 10-3 and 10-2 s-1)
showed that strain rates affected the tensile properties significantly.
At higher strain rates the strength was better but ductility was poor.
Microstructures of broken specimens showed that both the void
coalescence and the interface debonding affect the fracture behavior
of the alloys