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S. Arthanari et al.
the refined microstructure and fine dispersion of the second phases of laser surface
melted MB26 and AZ80 alloys were mainly responsible for the improved microhardness and corrosion resistance [37]. Rakesh et al. have reported that the laser
surface melting of Mg-1Zn-2Dy alloy with varying the laser energy densities (12.5
to 45 J/mm
2 ) improved its properties for resorbable implant applications [38]. The
melted layer has consisted of α-Mg and eutectic Mg 8 ZnDy phase with fine grains in
the order of 1-2 μm and columnar grains near the liquid-solid substrate due to the
cooling and the solidification rate was also identified. The microstructural refinement
and solid solution strengthening resulted in a better microhardness, furthermore, the
in vitro degradation rate through weight loss measurement was also decreased by
about 72% for 45 J/mm
2 laser melted alloy in Hank’s balanced salt solution.
LSM of Mg-5Ca-1Zn alloy using a femtosecond laser with varying pulse repetition
frequency (62.5, 500, 1000 Hz) revealed a significant variation in the second phase
fraction. The alloy treated with 500 Hz exhibited about a 63.3% reduction of Mg 2 Ca
phase, therefore, decreased the galvanic corrosion and enhanced the corrosion resistance in the HBSS solution. Furthermore, no significant change in the microhardness
values was noticed since the melted layer thickness values were only 2 ~ 3 μm and
500 Hz treated alloy exhibited higher cell viability compared to other treatments
[39]. Mg-2.2Zn alloys treated with varying the laser power and scan speed resulted
in refined microstructural features. However, the average surface roughness values
were increased due to the variation in the cooling rate and overlap region [40]. The
corrosion rates of LSM treated samples were increased compared to the untreated
alloy. However, the corrosion rates were decreased from 1 mm/y to 0.65-0.52 mm/y
for the LSM treated alloy after polishing and it was attributed to the microstructural
refinement and biomineralization during immersion in HBSS solution which acted
as a protective layer. These findings suggest that though the microstructural refinement contribute to the better surface properties, their micro/nanoscale features are
important to achieve better properties of the laser-treated samples.
The dissolution and re-distribution of second phases present in the as-received
alloy during the LSM are important aspects that enhance the in vitro properties of
Mg alloys. LSM treatment of Mg-6Gd-0.6Ca alloy enhanced the corrosion resistance,
cell attachment, and proliferation [41]. The improved corrosion resistance was mainly
attributed to the dissolution of the β-Mg 5 Gd phase in the melted region, which could
significantly reduce the galvanic corrosion. The cell attachment studies carried out
up to 24 h also revealed good adhesion, spreading, and proliferation on the laser
melted surface. LSM treated WE43 alloy was also revealed dissolution of alloying
elements and re-distribution of the second phase with the melted layer depth of
about 1.15 mm [42]. LSM treated AZ31 alloy with varying laser energy from 1.06
to 3.18 J/mm
2 produced melted layers with the thickness in the range from 125 to
199 μm. Furthermore, the number of second phase β-Mg 17 Al 12 was also increased in
the melted layer compared to the as-cast alloy, which could act as a barrier to corrosion
[43]. The redistribution of the β-Mg 17 Al 12 could be attributed to the re-heating of
the melted region during subsequent passes. These results show that the presence of
alloying elements alters the second phase segregation and grain refinement during
the LSM process.
S. Arthanari et al.
the refined microstructure and fine dispersion of the second phases of laser surface
melted MB26 and AZ80 alloys were mainly responsible for the improved microhardness and corrosion resistance [37]. Rakesh et al. have reported that the laser
surface melting of Mg-1Zn-2Dy alloy with varying the laser energy densities (12.5
to 45 J/mm
2 ) improved its properties for resorbable implant applications [38]. The
melted layer has consisted of α-Mg and eutectic Mg 8 ZnDy phase with fine grains in
the order of 1-2 μm and columnar grains near the liquid-solid substrate due to the
cooling and the solidification rate was also identified. The microstructural refinement
and solid solution strengthening resulted in a better microhardness, furthermore, the
in vitro degradation rate through weight loss measurement was also decreased by
about 72% for 45 J/mm
2 laser melted alloy in Hank’s balanced salt solution.
LSM of Mg-5Ca-1Zn alloy using a femtosecond laser with varying pulse repetition
frequency (62.5, 500, 1000 Hz) revealed a significant variation in the second phase
fraction. The alloy treated with 500 Hz exhibited about a 63.3% reduction of Mg 2 Ca
phase, therefore, decreased the galvanic corrosion and enhanced the corrosion resistance in the HBSS solution. Furthermore, no significant change in the microhardness
values was noticed since the melted layer thickness values were only 2 ~ 3 μm and
500 Hz treated alloy exhibited higher cell viability compared to other treatments
[39]. Mg-2.2Zn alloys treated with varying the laser power and scan speed resulted
in refined microstructural features. However, the average surface roughness values
were increased due to the variation in the cooling rate and overlap region [40]. The
corrosion rates of LSM treated samples were increased compared to the untreated
alloy. However, the corrosion rates were decreased from 1 mm/y to 0.65-0.52 mm/y
for the LSM treated alloy after polishing and it was attributed to the microstructural
refinement and biomineralization during immersion in HBSS solution which acted
as a protective layer. These findings suggest that though the microstructural refinement contribute to the better surface properties, their micro/nanoscale features are
important to achieve better properties of the laser-treated samples.
The dissolution and re-distribution of second phases present in the as-received
alloy during the LSM are important aspects that enhance the in vitro properties of
Mg alloys. LSM treatment of Mg-6Gd-0.6Ca alloy enhanced the corrosion resistance,
cell attachment, and proliferation [41]. The improved corrosion resistance was mainly
attributed to the dissolution of the β-Mg 5 Gd phase in the melted region, which could
significantly reduce the galvanic corrosion. The cell attachment studies carried out
up to 24 h also revealed good adhesion, spreading, and proliferation on the laser
melted surface. LSM treated WE43 alloy was also revealed dissolution of alloying
elements and re-distribution of the second phase with the melted layer depth of
about 1.15 mm [42]. LSM treated AZ31 alloy with varying laser energy from 1.06
to 3.18 J/mm
2 produced melted layers with the thickness in the range from 125 to
199 μm. Furthermore, the number of second phase β-Mg 17 Al 12 was also increased in
the melted layer compared to the as-cast alloy, which could act as a barrier to corrosion
[43]. The redistribution of the β-Mg 17 Al 12 could be attributed to the re-heating of
the melted region during subsequent passes. These results show that the presence of
alloying elements alters the second phase segregation and grain refinement during
the LSM process.