The microstructural characteristics and mechanical properties of rotary melting furnace processed aluminium alloyed ductile irons were investigated in this study. This was aimed at developing high performance -low material and processing cost ductile irons, suitable for the production of automobile components. Different compositions of the alloys were processed containing 1-4 wt.% aluminium. X-ray diffractometry, optical, scanning electron microscopy and mechanical properties measurements, were used to characterize the alloys. The results show that the ductile irons consists essentially, nodular and vermicular graphite-type distributed in a predominantly pearlite -ferrite matrix structures which attest to the viability of rotary furnace melt processing for ductile iron production. The nodule count were observed to increase with increase in Al wt.% but nodule sizes and degree of sphericity decreased with increase in Al wt.%. The mechanical properties of the ductile irons increased with increase in Al wt.%, except the ductility which decreased slightly with increase in Al wt.%.

Abstract:The corrosion of heat-treated Electroless-Nickel (EN) plated mild carbon steel (MCS) in dilute H 2 SO 4 is investigated and reported in the study. The MCS samples were electroless-Ni plated in alkaline Nimudeen 850. EN plated samples were soaked at different selected temperatures between 150-370 °C at constant time. The weight loss of the specimens by full immersion method was employed to assess the corrosion damage and corrosion rates of the as-received, EN plated MCS and four heat treated EN plated samples in the 0.5 M H 2 SO 4 solution. The test specimens were regularly examined at every 12 hrs interval for 30 days (720 hrs). The materials corrodes in 0.5 M H 2 SO 4 in the order of MCS10 > MCS14 > MCS15 > MCS11 > MCS13 > MCS12. Based on the results obtained, it will be justified to choose EN-plated samples (MCS 11) and the heat treated EN film (MCS12 and MCS13) for the purposed of solving the problem of corrosion in the medium. This is because; the application of EN deposition reduced the corrosion of MCS at much lower rate than the heat-treated EN film (MCS14 and MCS15) in 0.5 M H 2 SO 4 environment. Atomic Absorption Spectrometer (AAS) Thermo series 2000 model and Scanning Electron Microscopy (SEM) with the Energy Dispersive X-Ray (EDX) facilities (Jeol JSM-7600F model) were used to ascertain the chemical compositions and the microstructures of samples.

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.

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