Microstructure, tensile properties and electrochemical behavior of Pb alloy-45Â vol.% fly ash microballoon composites

Stir casting method was successfully employed to synthesis Pb-Ca-Sn alloys based composites containing high volume fraction (45 vol.%) of nickel-coated fly ash microballoons. Metallographic examinations showed that the presence of the fly ash microballoons in the Pb matrix alloys affected the matrix microstructures; the microstructure of the Pb alloy based composites revealed refinement effect in the matrix. The matrix areas near to the microballoons showed more refinement effect than the areas far away from the microballoons. Microstructure investigations, XRD analyses and EDAX results of the composites demonstrated that no significant reactions occurred at the interface between the microballoons and Pb matrix alloys. Density measurements showed that the addition of 45 vol.% of fly ash microballoons into Pb alloys significantly decreased the density of the composites. The yield and ultimate tensile stress of the composites were lower than those of the Pb matrix alloys. Also, the addition of fly ash microballoons into Pb alloys led to reduce significantly the strain to failure of the Pb based composites. However, the composites exhibited higher modulus of elasticity in comparison to those of the Pb matrix alloys. Investigations of the composite tensile fracture surfaces suggested that the combination of fly ash interfacial debonding and propagation of the crack through the matrix led to the final fracture of the composite. The experimental results showed that Pb-0.06 Ca-1.2 Sn-45 vol.% fly ash microballoon composite had the lowest specific resistance (0.0385 × 10−4 mΩ m2) in comparison with the other composites and matrix alloys. Also, the oxidation transient duration of this composite to form PbSO4 was the longest one (900 s), using polarization current density of 0.26 × 104 mA m−2 recorded at −400 mV versus Hg/Hg2SO4 electrode.