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M. S. Dani and I. B. Dave
of grain size number of FSPed AZ91 Mg alloy with aluminum powder SP and DP
with 380 and 545 rpm with untreated die-cast AZ91 Mg alloy.
Thus, the hardness profile of the specimens produced with DP FSP is smoother
than that in the SP FSPed specimen in both rotational speed 380 and 545 rpm with
aluminum powder. Uniform distributed aluminum clusters result in a uniform hardness profile in DP. Maximum grain refinement in the case of FSP with aluminum
powder DP may be attributed to the presence of reasonably uniformly distributed
aluminum particles which act as nuclei and also restrict grain growth during solidification. The eutectic β-phase (Mg 17 Al 12 ) in die-cast AZ91 Mg alloy was disappeared
after FSP because stir zone temperature exceeds the dissolution temperature of βphase (Mg 17 Al 12 ) in Mg matrix, and the refinement of grain size is affected by
the FSP parameters like rotational speed, transverse speed, no. of passes, etc. The
grain structure in SZ had fine and equiaxed grains due to recrystallization. Thus,
FSP grain refinement and homogeneity of surface were achieved by dissolution of
β-phase (Mg 17 Al 12 ).
4 Conclusions
1. AZ91 Mg alloy FSP resulted in the structural modification and grain refinement
as well as slight hardness improvement.
2. Pure aluminum powder can be successfully used as reinforcement in FSP.
3. FSP parameters like as rotational speed, transverse speed, reinforcement materials and the number of passes affect the refinement of grain size and particle
distribution pattern during process.
4. The microstructures in the FSP DP with aluminum powder can be refined to a
much smaller scale than FSP single-pass and die-cast AZ91 Mg alloy because
of more precipitation of the β-phase (Mg 17 Al 12 ). The recrystallized grains were
equiaxed and have a smaller size distribution. Aluminum powder was found to
be distributed within the region due to vigorous stirring during FSP at 545 rpm.
5. FSP single pass with aluminum powder has nonuniform distribution, while FSP
double pass with aluminum powder has a uniform distribution of aluminum
powder. The results show that FSP DP with aluminum powder has an improvement in hardness and fine grain refinement compared to FSP SP with aluminum,
FSP SP and DP without aluminum powder and die-cast AZ91 Mg alloy which
further improves by increasing rotational speed.
6. The grain structure in SZ had fine and equiaxed grains due to recrystallization.
Acknowledgements The authors are grateful for conducting FSP work at Mechanical department,
School of Technology Pandit Deendayal Petroleum University (PDPU) and Facilitation Center for
Industrial Plasma Technologies (FCIPT) for guidance and utilization of characterization facilities.
M. S. Dani and I. B. Dave
of grain size number of FSPed AZ91 Mg alloy with aluminum powder SP and DP
with 380 and 545 rpm with untreated die-cast AZ91 Mg alloy.
Thus, the hardness profile of the specimens produced with DP FSP is smoother
than that in the SP FSPed specimen in both rotational speed 380 and 545 rpm with
aluminum powder. Uniform distributed aluminum clusters result in a uniform hardness profile in DP. Maximum grain refinement in the case of FSP with aluminum
powder DP may be attributed to the presence of reasonably uniformly distributed
aluminum particles which act as nuclei and also restrict grain growth during solidification. The eutectic β-phase (Mg 17 Al 12 ) in die-cast AZ91 Mg alloy was disappeared
after FSP because stir zone temperature exceeds the dissolution temperature of βphase (Mg 17 Al 12 ) in Mg matrix, and the refinement of grain size is affected by
the FSP parameters like rotational speed, transverse speed, no. of passes, etc. The
grain structure in SZ had fine and equiaxed grains due to recrystallization. Thus,
FSP grain refinement and homogeneity of surface were achieved by dissolution of
β-phase (Mg 17 Al 12 ).
4 Conclusions
1. AZ91 Mg alloy FSP resulted in the structural modification and grain refinement
as well as slight hardness improvement.
2. Pure aluminum powder can be successfully used as reinforcement in FSP.
3. FSP parameters like as rotational speed, transverse speed, reinforcement materials and the number of passes affect the refinement of grain size and particle
distribution pattern during process.
4. The microstructures in the FSP DP with aluminum powder can be refined to a
much smaller scale than FSP single-pass and die-cast AZ91 Mg alloy because
of more precipitation of the β-phase (Mg 17 Al 12 ). The recrystallized grains were
equiaxed and have a smaller size distribution. Aluminum powder was found to
be distributed within the region due to vigorous stirring during FSP at 545 rpm.
5. FSP single pass with aluminum powder has nonuniform distribution, while FSP
double pass with aluminum powder has a uniform distribution of aluminum
powder. The results show that FSP DP with aluminum powder has an improvement in hardness and fine grain refinement compared to FSP SP with aluminum,
FSP SP and DP without aluminum powder and die-cast AZ91 Mg alloy which
further improves by increasing rotational speed.
6. The grain structure in SZ had fine and equiaxed grains due to recrystallization.
Acknowledgements The authors are grateful for conducting FSP work at Mechanical department,
School of Technology Pandit Deendayal Petroleum University (PDPU) and Facilitation Center for
Industrial Plasma Technologies (FCIPT) for guidance and utilization of characterization facilities.