Friction, Wear and Mechanical Properties of Al-Si LM6 Cast Alloy Processed in Semi-solid Stage

Abstract

Dry sliding wear characteristics, mechanical properties and microstructural behavior of powder-chip based reinforcement silicon rich LM6 aluminum alloy, fabricated by semi-solid casting were investigated. Wear tests were conducted on powder-chip reinforced cast samples using the pin on disc apparatus under 5, 10 and 15 N with 0.4, 0.8 and 1.2 m/s sliding speeds for 250, 500 and 750 m sliding distances versus EN31 tool steel hardened to 62 HRC. An observation from the microstructure images indicated that the porosity of the cast composite reduces due to the distribution of un-melted chips inside the short cavities by the addition of reinforcement and confirmed with the obtained results of density. The fracture in cast specimens indicates that the micro-cracks were prevalently propagated along the broken eutectic silicon particles. Additionally, wear resistance was increased reasonably due to the inclusion of reinforcement under metallic wear environment. Worn surfaces SEM, EDS, XRD and, AFM analysis suggests that surfaces plastically deformed along with silicon brittle asperities which stuck on the softer surface of the contact layers, while dominant wear mechanisms were found from these surfaces and wear debris.

Appendix

Worn out specimens were taken for measurement of weight loss with an accuracy of ± 0.0001 mg after end of each operation. Specific wear rate ‘k’ (mm³/Nm), was calculated by equation (1) and coefficient of friction ‘μ’ by equation (1) as:

$$ k = \frac{m}{F_{N} tV_{s} \rho} $$

(1)

$$ \mu = \frac{F_{T}} {F_{N}} $$

(2)

Here,

m = Specimen mass loss (g), ρ = Density of the pin material (g/cm³) , t = Time duration for the test (s), Vs = Sliding velocity (m/s) , F_N = Applied Load, and F_T = Tangential applied forces