Microstructural Characteristics, Mechanical and Wear Behaviour of Aluminium-Alloyed Ductile Irons Subjected to Two Austempering Processes

Abstract

The effect of aluminium addition and austempering processes on the microstructures, mechanical and wear properties of rotary melting furnace processed ductile irons was investigated. Ductile irons containing 1−4 wt.% Al were produced and subjected to single and two-step austempering processes. Optical microscopy was used to characterize the graphite features and estimate the volume fraction of the matrix phases present, while the x-ray diffractogram was also carried out to analyse the samples. Mechanical and wear properties of the alloys were equally evaluated. From the results, it was observed that both the as-cast and austempered ductile iron microstructures contained nodular graphite, and the matrix structure for the as-cast ductile irons consisted predominantly of pearlite and ferrite, while that of the austempered grades, contained principally, ausferrite. The microstructure and intermetallic compound obtained played dominant role on the properties of the alloys. The aluminium addition and austempering processes had a significant influence on the mechanical properties and wear resistance of the alloys. The austempered ductile irons exhibited superior strength and wear resistance compared to the as-cast samples, albeit ductility values were lower in the composition group. Austempering increased the strength by over 100% while the addition of Al further enhanced the strength. The improved properties were linked to the refined microstructure, increased proportion of ausferrite phase and intermetallic compound formed. For all properties evaluated, the two-step austempering yielded better properties combination than the single step process. The rotary melting furnace processing adopted was found viable for ductile iron production.

Effects of aluminium addition and austempering temperatures on Al-alloyed ductile iron microstructure and mechanical properties

“…Moreover, all heattreated microstructures showed graphite nodules and carbides immersed in an ausferritic matrix of the Al-alloyed austempered ductile cast irons (AADCI) with no variations observed on their characteristics [1,6,23]. The earlier works of Adebayo et al [12,23] had reported the presence of theformation of some intermetallics compounds which showed the presence of Al-carbide phases in all the samples that contain Al as indicated in the form of intermetallic compounds of Al such as Al4SiC4,Al4C3 and MgAl2C2; in addition to Fe3C and Fe2C. This correlates and validates the carbide formation reported by Pimentel [26] on Niobium carbide and Chromium carbides (as eutectic of M3C) that were formed from the addition of Nb and Cr to cast iron.…”

“…Diverse works on various properties of austempered ductile cast iron (ADCI) and Aluminium-alloyed austempered ductile cast iron (AADCI) have been widely circulated. These include contact and bending fatigue behaviour; microstructure and abrasion wear behavior, wear and friction behaviors [12]. Pereira et al [13]studied the mechanical properties such as ultimate tensile strength (UTS), yield strength (YS), elongation); Brinell hardness (HB) and microstructures of austempered ductile cast iron (ADCI) alloyed with Cu-Ni-Mn-Mo in hot air austempering cycles in a two-step mechanism.…”

Microstructural Evolution as a Function of Increasing Aluminum Content in Novel Lightweight Cast Irons

“…%, and 3.74 wt. % Al [24]. Ibrahim et al [18] studied the hardness, oxidation resistance and damping capacity of Al-alloyed (up to 16 wt.…”