Bimetallic AZ91/AlSi17 samples were produced by compound casting. The casting process involved pouring the AZ91 magnesium alloy heated to 650oC onto a solid AlSi17 aluminum alloy insert placed in a steel mould. Prior to casting, the mould with the insert inside was heated to about 370oC. The bonding zone formed between AZ91 and AlSi17 had a thickness of about 200 μm; it was characterized by a non-homogeneous microstructure. Two different areas were distinguished in this zone: the area adjacent to the AZ91 and the area close to the AlSi17. In the area closest to the AZ91 alloy, a eutectic composed of an Mg17Al12 intermetallic phase and a solid solution of Al in Mg was observed. In bonding zone at a certain distance from the AZ91 alloy an Mg2Si phase co-occurred with the eutectic. In the area adjacent to the AlSi17 alloy, the structure consisted of Al3Mg2, Mg17Al12 and Mg2Si. The fine Mg2Si phase particles were distributed over the entire Mg-Al intermetallic phase matrix. The microhardness of the bonding zone was much higher than those of the materials joined; the microhardness values were in the range 203-298 HV. The shear strength of the AZ91/AlSi17 joint varied from 32.5 to 36 MPa.
This paper discusses the joining of AZ91 magnesium alloy with AlSi17 aluminium alloy by compound casting. Molten AZ91 was cast at
650oC onto a solid AlSi17 insert placed in a steel mould under normal atmospheric conditions. Before casting, the mould with the insert
inside was heated up to about 370oC. The bonding zone forming between the two alloys because of diffusion had a multiphase structure
and a thickness of about 200 µm. The microstructure and composition of the bonding zone were analysed using optical microscopy,
scanning electron microscopy and energy dispersive X-ray spectroscopy. The results indicate that the bonding zone adjacent to the AlSi17
alloy was composed of an Al3Mg2 intermetallic phase with not fully consumed primary Si particles, surrounded by a rim of an Mg2Si
intermetallic phase and fine Mg2Si particles. The bonding zone near the AZ91 alloy was composed of a eutectic (an Mg17Al12 intermetallic
phase and a solid solution of Al and Si in Mg). It was also found that the compound casting process slightly affected the AZ91alloy
microstructure; a thin layer adjacent to the bonding zone of the alloy was enriched with aluminium.
Al-enriched layer was formed on a magnesium substrate with use of casting. The magnesium melt was cast into a steel mould with an
aluminium insert placed inside. Different conditions of the casting process were applied. The reaction between the molten magnesium and
the aluminium piece during casting led to the formation of an Al-enriched surface layer on the magnesium substrate. The thickness of the
layer was dependent on the casting conditions. In all fabricated layers the following phases were detected: a solid solution of Mg in Al,
Al3Mg2, Mg17Al12 and a solid solution of Mg in Al. When the temperature of the melt and the mould was lower (variant 1 – 670o
C and 310 o
; variant 2 – 680o
C and 310o
C, respectively) the unreacted thin layer of aluminium was observed in the outer zone. Applying higher
temperatures of the melt (685o
C) and the mould (325o
C) resulted in deep penetration of aluminium into the magnesium substrate. Areas
enriched in aluminium were locally observed. The Al-enriched layers composed mainly of Mg-Al intermetallic phases have hardness from
187-256 HV0.1.
Flake graphite cast iron was hot-dip coated with pure aluminium or aluminium alloys (AlSi11 and AlTi5). The study aimed at determining
the influence of bath composition on the thickness, microstructure and phase composition of the coatings. The analysis was conducted by
means of an optical microscope and a scanning electron microscope with an EDS spectrometer. It was found that the overall thickness of a
coating was greatly dependent on the chemical composition of a bath. The coatings consisted of an outer layer and an inner intermetallic
layer, the latter with two zones and dispersed graphite. In all the cases considered, the zone in the inner intermetallic layer adjacent to the
cast iron substrate contained the Al5Fe2 phase with small amount of silicon; the interface between this phase and the cast iron substrate
differed substantially, depending on the bath composition. In the coatings produced by hot-dipping in pure aluminium the zone adjacent to
the outer layer had a composition similar to that produced from an AlTi5 bath, the Al3Fe phase was identified in this zone. The Al3Fe also
contained silicon but its amount was lower than that in the Al5Fe2. In the coatings produced by hot-dipping in AlSi11, the zone adjacent to
the outer layer contained the Al3FeSi phase. The analysis results showed that when AlSi11 alloy was applied, the growth mode of the inner
layer changed from inwards to outwards. The interface between the Al5Fe2 phase and the cast iron substrate was flat and the zone of this
phase was very thin. Locally, there were deep penetrations of the Al5FeSi phase into the outer layer, and the interface between this phase
and the outer layer was irregular. Immersion in an AlTi5 bath caused that the inner intermetallic layer was thicker than when pure
aluminium or AlSi11 alloy baths were used; also, some porosity was observed in this layer; and finally, the interface between the inner
layer and the cast iron substrate was the most irregular.