Inquiry regarding the reduction of hardness value at the center of nugget for friction stir welded SiC particle reinforced Al matrix composite material.
Here I have attached the variation of hardness of samples (hardness taken through out the center of the nugget from one side of the base material to the other side. An unusual observation is made here that at the center of nugget there is a steep decrease in hardness, which is contrary to the general observation with increase in hardness value at the center of nugget. Kindly suggest me some possibilities behind such observation. Your valuable advises will be very much helpful for me to proceed further.
The microhardness of composites is determined by reinforcing particles distribution and not by the fine grained structure of the matrix metal. You should analyze the SiC particles distribution across the microhardness profile. Sometimes higher number of SiC particles is found closer to advancing side of the weld.
Dear Uttam Acharya,
The reduction in microhardness values in the center of your sample may be explained by the dilution of the reinforcing particles at the center of nugget, which would lead to the formation of transition zones between a hard matrix and a soft matrix zone (giving rise to a lower hardness). I suggest doing a quantitative analysis of Sic's reinforcing particles in this area and comparing it with the surface of your samples where you found a large fluctuation in the microhardness data.
Best kinds
IDIR
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