Please see the attached reference, it's open access.

http://www.mdpi.com/2075-4701/4/1/65/htm#4PreparationMethodsandProperties

Stir casting is the widely adopted route for mixing reinforcements with molten metal. However, it is impossible to mix every kind of ceramic particle with molten metal due wettability issues. Many investigators used different techniques such as preheating of particles, adding wettability agents, coating of particles etc. In my experience, it is extremely difficult to obtain good dispersion except for SiC particles which has good wettability with molten metals. If nano particles are selected for reinforcement, it will multiply the challenges.  

Some reduced the temperature of the molten metal within the freezing range and added reinforcements to overcome wettability issues. This method is known as compocasting or slurry casting.

Instead of adding reinforcement, one can look into the generation of in-situ ceramic particles within the molten metal. This will give proper distribution and overcome the issues with wettability.

Another promising method to obtain good dispersion is squeeze casting. In this technique, ceramic precursor is infiltrated with molten metal under pressure. This method is commonly used for producing high volume fraction (>40%) of MMCs. 

Please refer the following publications from my research group which may give some ideas.

https://www.researchgate.net/publication/304704982_Prediction_of_influence_of_process_parameters_on_tensile_strength_of_AA6061TiC_aluminum_matrix_composites_produced_using_stir_casting?ev=prf_pub

https://www.researchgate.net/publication/257086718_Microstructure_and_some_mechanical_properties_of_fly_ash_particulate_reinforced_AA6061_aluminum_alloy_composites_prepared_by_compocasting

https://www.researchgate.net/publication/271636950_Synthesis_and_characterization_of_in_situ_formed_titanium_diboride_particulate_reinforced_AA7075_aluminum_alloy_cast_composites?ev=prf_pub

Article Prediction of influence of process parameters on tensile str...

Article Microstructure and some mechanical properties of fly ash par...

Article Synthesis and characterization of in situ formed titanium di...

Mixing of metal matrix composite requires some attentive points

1.Mesh Size of the reinforcement should be fine Grade

2.Proper Heating of reinforcement Material 

3.Addition of Magnesium in Uniform

4.Casting Should have an arrangement to pressurize

5.Metal Mould Casting Rote Should be Followed

6. Selection of Matrix Material Should of more magnesium content i.e Al-6063 series

Dear Dr. Dinaharan

Thank you so much for the deep insight into the techniques.

Can you please give some brief Idea about

"one can look into the generation of in-situ ceramic particles within the molten metal"

Dear RR Mishra,

Please go through the following review article which will give you ideas to generate various ceramic particles within the molten metal.

S.L. Pramod, S.R. Bakshi, B.S. Murty, Aluminum-Based Cast In Situ Composites: A Review, Journal of Materials Engineering and Performance 24 (2015) 2185–2207.

Following lecture also may help you

https://www.youtube.com/watch?v=buUrsvT9tB4

Thank you so much, Dr. Dinaharan.

Dear Mishra

Please refer the following links and publications which may help you.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwietq_QsLPSAhVLVhQKHVf-D7wQFggZMAA&url=https%3A%2F%2Fwww.ijsr.net%2Farchive%2Fv4i5%2FSUB154564.pdf&usg=AFQjCNGyhQXGWMMpaSPPakW90FkCckfnYw&sig2=E_FTgoT78FoO4iJyrbf40Q&bvm=bv.148073327,d.bGs

http://www.sciencedirect.com/science/article/pii/S092150930400348X

https://www.scirp.org/journal/PaperInformation.aspx?PaperID=7622

https://www.scientific.net/AMR.585.301

https://www.scirp.org/journal/PaperInformation.aspx?PaperID=27188

Article Synthesis and Characterisation of Al 7075 reinforced with Si...

Dear RRM

I hope many of them have already answered your Question  

one suggestion is you can check for two step stir casting 

you can check for a review paper on processing of MMCs  by Asthana  u may get all in one paper