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Physical grain refinement is examined under high-intensity ultrasonication during solidification in commercial purity Al (CP-Al) and binary Al-10wt.% Cu alloy melts cooled naturally in air and compared against chemical inoculation using Al-5Ti-1B grain refiner. The coarse dendritic unrefined base microstructure was completely replaced with a fine equiaxed grain structure in the case of either inoculation or ultrasonication. However, ultrasonication produced more effective refinement over chemical inoculation with a twofold and eight-fold increase in the grain density in CP-Al and Al-10%Cu alloy, respectively. While combining chemical inoculation with ultrasonication produced the finest grain structure in CP-Al, no further improvement over ultrasonication was noted for the Al-10%Cu alloy. Noticeable reduction in nucleation undercooling, of similar magnitude to chemical inoculation, was observed under ultrasonication. Cooling curve observations indicate strongly enhanced heterogeneous nucleation under ultrasonication. It appears that although chemical inoculation utilises higher potency nucleants, more nucleation events are favoured under cavitation.

Effect of Ni alloying on the microstructural evolution and mechanical properties of two duplex lightweight steels during different annealing temperatures : experiment and phase-field simulation. Acta Materialia.

In this study we consider the effect of separately adding 0.5 wt.% to 1.5 wt.% Zn or 0.5 wt.% to 2 wt.% Al to the eutectic Sn-3.5Ag lead-free solder alloy to limit intermetallic compound (IMC) growth between a limited volume of solder and the contact metallization. The resultant solder joint microstructure after reflow and high-temperature storage at 150°C for up to 1000 h was investigated. Experimental results confirmed that the addition of 1.0 wt.% to 1.5 wt.% Zn leads to the formation of Cu-Zn on the Cu substrate, followed by massive spalling of the Cu-Zn IMC from the Cu substrate. Growth of the Cu 6 Sn 5 IMC layer is significantly suppressed. The addition of 0.5 wt.% Zn does not result in the formation of a Cu-Zn layer. On Ni substrates, the Zn segregates to the Ni 3 Sn 4 IMC layer and suppresses its growth. The addition of Al to Sn-3.5Ag solder results in the formation of Al-Cu IMC particles in the solder matrix when reflowed on the Cu substrate, while on Ni substrates Al-Ni IMCs spall into the solder matrix. The formation of a continuous barrier layer in the presence of Al and Zn, as reported when using solder baths, is not observed because of the limited solder volumes used, which are more typical of reflow soldering.