Effects on surface properties of the hot dip aluminum coated parts which were produced iron-based powder metallurgy

In this study, iron based PM aluminum coated by using hot-dip aluminizing method. Dipping time , bath temperature and chemical composition variable effects were investigated on coating thickness and structures of hot-dip aluminum process. For that purpose , four different group of iron based PM samples were produced according to different carbon rate in compositions and were dipped in Etial 171 aluminum bath under argon gas cover, at 5 min. - 30 sec dipping time and at 700 °C - 750 °C temperature. Aluminum coating thickness and structure were investigated by using metallographic and microscopic techniques and chemical composition of coating determined by using EDS analyses on SEM images. According to metallographic studies, aluminum coating on iron based PM samples consist of two layer, aluminum coating at outer surface and inferior intermetallic compound. EDS analyses proof that coating process is a diffusion mechanism. During dipping, because of high energy level of aluminum atoms are advancing through PM and forming band shape intermetallic structure with iron atoms. Observed that, dipping time and bath temperature parameters has a strong effects on forming of intermetallic compound which also effective on diffusion mechanism. According to results, this intermetallic layer thickness increasing with raising temperature. After reaching optimum temperature level, there is no change observed in thickness with increasing temperature, but contrary almost stay constant. Similar effects can be say for while forming of aluminum coating on intermetallic layer. With the increasing of the temperature, the thicknesses of the aluminum coating were increased. At the beginning; coating layer thickness increased with longer dipping time. But later increase slow down and almost stay constant. Time dependent increasing on coating thickness raise is matching parabolic speed law. With increasing dipping time and related coating thickness observed that, there is a crack occurrence and gap propagating in micro structure those are resulting splitting in coating layer. Chemical composition effects on coating thickness also determined with experimental. While carbon rate increasing in chemical composition of PM, also trigger a little increasing on intermetallic layer thickness.PM and Aluminized PM samples had been examined under same intensive salt environment to defining corrosion resistance properties. For that purpose, uncoated PM samples at 7 day and coated PM samples tested at along 90 day in the corrosion incubator. At the end of the test, mass lost was measured from samples and investigated micro structural propagating of corrosion on PM samples by using metallographic and microscopic techniques.Experimental results prove that chemical composition of iron based PM, has no effects on corrosion or corrosion resistance and hot dip aluminized PM samples showed that has strong corrosion resistance than uncoated samples. While surface of the uncoated PM samples pitting type of corrosion advance, white colored aluminum oxide observed on aluminized PM samples. According to microscopic investigations and metallographic studies, aluminum oxide propagated on surface micro cracks and pitting type of corrosion on aluminum layer also propagating, but in the other hand mentioned hard aluminum oxide saved beneath of PM sample from aggressive corrosion environment.With the intention of improve hot dip aluminum coating properties, the samples had investigated which were has got flaw on coating. According to metallographic studies, coating come apart from outer surface because of stamping and crack. This splitting and come outs from surface determined because of micro structural flaws such as porosity and micro-cracks. Such discovery prove that in any case of dirt or oxide remaining on surface of PM or aluminum bath, or insufficient inert argon gas cover on aluminum bath, during dipping cause a forming of such micro structural flaws on coatings.