Effects of gadolinium addition on the microstructure and mechanical properties of Mg–9Al alloy

This research aims to study the significance of Gd addition(0wt%–2wt%) on the microstructure and mechanical properties of Mg–9Al alloy. The effect of Gd addition on the microstructure was investigated via X-ray diffraction(XRD), optical microscopy, scanning electron microscopy(SEM), and transmission electron microscopy(TEM). The Mg–9Al alloy contained two phases, α-Mg and β-Mg_(17)Al_(12). Alloying with Gd led to the emergence of a new rectangular-shaped phase, Al_2Gd. The grain size also decreased marginally upon Gd addition. The ultimate tensile strength and microhardness of Mg–9Al alloy increased by 23% and 19%, respectively, upon 1.5wt% Gd addition. We observed that, although Mg–9Al–2.0Gd alloy exhibited the smallest grain size(181 μm) and the highest dislocation density(5.1 × 10^(10) m^(-2)) among the investigated compositions, the Mg–9Al–1.5Gd alloy displayed the best mechanical properties. This anomalous behavior was observed because the Al_2Gd phase was uniformly distributed and present in abundance in Mg–9Al–1.5Gd alloy, whereas it was coarsened and asymmetrically conglomerated in Mg–9Al–2.0Gd.

Microstructure and mechanical properties of gadolinium-and misch metal-added Mg-Al alloy

The study investigates the effects of individual and combined additions of gadolinium(Gd)and misch metal(MM)on the microstructure and mechanical properties of Mg-4Al and Mg-9Al alloys.The results show that the additions significantly alter the microstructure and grain size of the base alloys.Mg-4Al based alloys have globular morphology,whereas Mg-9Al based alloys have dendritic morphology.The addition of alloying elements,Gd and MM,introduces rectangular-shaped Al_(2)Gd phase and needle-shaped Al_(11)RE_(3) phase,respectively.The best mechanical properties at room temperature are shown by Mg-9Al-2Gd alloy with tensile strength and elongation of 214 MPa and 6.0%,respectively,whereas Mg-4Al-2Gd alloy exhibits the best properties at elevated temperature(150℃)with tensile strength and elongation of 172 MPa and 14.0%,respectively.The study also reports the microhardness value of different phases along with the cast alloys.Eutectic Mg_(17)Al_(12) phase shows the highest hardness(VHN 92)followed by lamellar Mg17Al12(VHN 83)andα-Mg matrix(VHN 68).

Analyzing the Effects of Milling and Sintering Parameters on Crystalline Phase Evolution and Mechanical Properties of Al_(86)Ni_(8)Y_(6) and Al_(86)Ni_(6)Y_(4.5)Co_(2)La_(1.5) Amorphous Ribbons

In the present study,Al_(86)Ni_(8)Y_(6) and Al_(86)Ni_(6)Y_(4.5)Co_(2)La_(1.5) bulk amorphous nanocomposites were synthesized by spark plasma sintering of milled melt spun ribbon particles.The as-cast ribbons were of near amorphous nature with minute amount of FCC Al embedded in the amorphous matrix.Milling of the ribbons resulted in partial devitrifi cation due to mechanical crystallization.The milled ribbon particles were sintered in the temperature and pressure range of 300-500℃ and 500-700 MPa,respectively.It was observed that nominal amount of amorphous phase was retained at 500℃ and 500 MPa.With increase in sintering pressure and decrease in sintering temperature,the amount of crystalline phase evolution decreased,and maximum amount of amorphous phase was retained at 300℃ and 700 MPa.The microstructure consisting of amorphous phase embedded with hard intermetallic phases led to increase in the nanohardness of Al_(86)Ni_(8)Y_(6) and Al_(86)Ni_(6)Y_(4.5)Co_(2)La_(1.5) as-cast ribbons from 3.26±0.59 GPa and 3.81±0.58 GPa to 6.06±0.70 GPa and 6.14±0.82 GPa,respectively,for the corresponding consolidated amorphous nanocomposite.Microhardness of the three and five component system bulk samples was 4.19±0.13GPa and 3.6±0.13 GPa,respectively.

Effect of Sintering Temperature and Heating Rate on Crystallite Size,Densification Behaviour and Mechanical Properties of Al-MWCNT Nanocomposite Consolidated via Spark Plasma Sintering

Powder mixture of ball-milled aluminium and functionalized multi-walled carbon nanotubes was compacted via spark plasma sintering （SPS） to study effects of sintering temperature and heating rate. An increase in sintering temperature led to an increase in crystallite size and density, whereas an increase in heating rate exerted the opposite effect. The crystallite size and relative density increased by 85.0% and 14.3%, respectively, upon increasing the sintering temperature from 400 to 600℃, whereas increasing the heating rate from 25 to 100 ℃/min led to respective reduction by 30.0% of crystallite size and 1.8% of relative density. The total punch displacement during SPS for the nanocomposite sintered at 600 ℃ （1.96 mm） was much higher than that of the sample sintered at 400 ℃ （1.02 mm） confirming positive impact of high sintering temperature on densification behaviour. The maximum improvement in mechanical properties was exhibited by the nanocomposite sintered at 600 ℃ at a heating rate of 50℃/min displaying microhardness of 81 4- 3.6 VHN and elastic modulus of 89 4- 5.3 GPa. The nanocomposites consolidated at 400 ℃ and 100 ℃/min, in spite of having relatively smaller crystallite size, exhibited poor mechanical properties indicating the detrimental effect of porosity on the mechanical properties.