Is the formation of the Intermetallics like Mg2Si considered as a necessity to call the resultant product "Metal Matrix composite", or even if those intermetallics (Mg2Si in particular) are Not detected in XRD patterns, but SEM photos show good bonding between Mg and Sic particles, wear properties show substantial enhancement , and hardness increased, the result of the process would be acceptable.
For example, so as to clarify the question, in the case of Cu/Sic processed by friction stir processing there is no intermetallics formed ( Between Cu and Sic) but, the authors consider aforementioned enhanced features sufficient to claim a successful process.
Different things are: Composites and Hybrid composites. Composites, themselves, can be so finely interconnected that can be defined as fine as nano-composites but not yet hybrids.
I would suggest that the formation of Mg2Si could be considered the formation of a Hybrid composite, because they change their original state to form a new one with the other chemical species.
In your case, as you state, by putting together independent particles, you obtain a new system, still characterised by separated particles but interconnected by strong interconnecting forces. This new system can be defined a Composite.
I belive that you are in the position to define your system a metal-matrix composite.
No it is not a compulsory, as you write that SEM pics show good bonding between particle it is already intermetallic of Mg and Si but for more clarification you can go for TEM analysis and indexing of the SAED pattern make it more clear, I hope your problem will be short out.
On the contrary, the evidence you have by showing strengthening and strong distinguished interfaces is enough for a MMC, but what we do is we check if other precipitates have formed to complete the study like sometimes carvides form in Al alloys. so the answer is no the formation of Mg2Si is not a must to confirm that your new developed material is a composite.
Dear Morteza,
In general it is not necessary to have a strong chemical reaction between the matrix and the reinforcement, as for instance the formation of intermetallic compounds, to consider the material as a metal matrix composite, particularly in the case of light alloys like Al and Mg alloys.
Some adhesive behaviour, usually involving some reaction and interdiffusion between matris and particles or fibres isrecommended to enhace the charge transfer between matrix and reinforcement. However some times (I have verified it) the formation of intermetalic compounds means a too strong reaction producing the degradation of the reinforced fibres (for instance), or even the development of very brittle and coarse intermetallic particles at the interface, which degradate the mechanical properties of the MMC..
So, the formation of intermetallics in MMC, not only are not a requirement but even in some case should be avoided.
I hope that this could be useful for you
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