Study on Low Cycle Fatigue and Tensile Behavior of Al 5083/CNT/MoB/Ni Hybrid Composite

1. Introduction

Al 5083 is an Al-Mg alloy which contains 4-4.9 wt% Mg. It is a non-heat treatable, medium strength wrought aluminium alloy in which strength of the alloy increases with increase in Mg content. The alloy has a remarkable combination of resistance to corrosion, weldability and economy of fabrication, Huang et al. (2017). But for many industrial applications though, the fatigue performance of Al 5083 is a matter of concern for selection as structural material. Exploration of fatigue behavior of aluminium metal matrix composites with dynamic loading plays a vital role in material selection, forecasting the life of elements, design and its endurance.

Fatigue leads to deformation of components and ultimately to failure. The operating repeated stresses for the materials may be less than the static strength but the crack generating under the repeated stress causes the rupture, Aydin et al. (2018). Microstructure of the material and the exposed environment has deciding influence on crack growth due to fatigue, Xiaoyan et al. (2016). The microstructure of components will deteriorate during the service life causing the fatigue rates to increase. The fatigue fracture includes three phases: a) crack nucleation and induction, b) crack propagation and c) sudden rupture. Most engineering materials include defects which are stress concentrators. The region of structural defects undergoes high deformation from where fatigue cracks initiates and grows. Extensive knowledge of fatigue properties requires interpretation of the fatigue crack growth, and such learning is still very few till date. In view of the life of the material the measurement of fatigue strength is a critical element.

Jian Feng et al. (2017) studied on Al-Ni alloy with different Ni weight percentages and reported that as Ni content increases ε-Al₃Ni weight fraction increases which results in increase in tensile strength and decrease in elongation. As the Ni content is increased to 4%, the coarsening of ε-Al₃Ni occurs resulting in acceleration of crack propagation causing decrease in fatigue strength. Mustafa and Necmettin (2017) reported increase in fatigue life for E glass/epoxy composite with the addition on CNT. They explained the bridging mechanism and mechanical interlocking of CNT fibres in stopping the propagation of cracks. The bridging effect of CNT is also recorded by Shin and Bae (2018) in their studies with Al 2024 reinforced with CNT. The pull-out mechanism of MWCNT is explained to be the reason for increased fatigue strength of the composite material. Kruzic et al. (2004) investigated the fatigue and fracture characteristics of three Mo–Si–B alloys having continuous α-Mo phase. They reported that the failure or degradation of bridges contributes to fatigue crack growth and ductile α-Mo phase promotes the crack advance. Wenlong et al. (2010) studied on the Al₂O_3f/Al composite wire and reported that the Ni–P coating could increase the fatigue resistance of the composite wire. They explained that the load bearing capacity of the broken fibres can be restored by Ni-P coating thus reducing the stress strain concentrations. Xiaoyan et al. (2016) studied annealing and normalizing heat treatments on Nickel Aluminium Bronze to produce different second phases. They noted that coarse dendritic K_II particles and hard brittle K_III lamellae phases in annealed sample promotes fatigue crack propagation whereas normalized samples having K_IV precipitates resists fatigue crack growth. Murayama et al. (1999) studied the combined influence of nitrogen and molybdenum in the fatigued micro structure of 316 austenic steel. The improved fatigue life reported is explained to be because of the strong Mo-N bonding which acts as a strong barrier for the dislocation motion.