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Co-Continuous Ceramic Composites (C4) have been fabricated through gas pressure infiltration technique with SiC foam reinforcement of 10PPI and 20PPI, and with AA5083 alloy as matrix. The fabricated composites (C4) were tested for mechanical properties at static condition. This study delineates the effect of pores per inch (PPI) of SiC foams on the mechanical properties of the composite. The 10PPI C4 composite with highest content of AA5083 (81%) exhibited a compressive strength of 131 MPa, 5% greater than 20PPI C4 composite. The C4 composite displayed 65 times higher compressive strength than SiC foam (~2 MPa). The compression failure mode was found to be shear failure and vertical splitting, with the SiC foam failing first, followed by failure of AA5083. A positive correlation was observed between the compressive strength and hardness of the composite, where 10PPI composite exhibits 56 BHN, and 20PPI with 50 BHN. Additionally, microstructural analysis was performed to characterize the interface morphology of SiC foam and AA5083 alloy.

Dry sliding wear behaviour of Al–4Mg alloy and Al–4Mg alloy/MgAl2O4 in situ composites was examined under normal loads of 10–30 N at sliding speeds of 1, 3, 5 and 7 m/s and sliding distance of 1500 m using a pin-on-disc apparatus. Al–4Mg alloy with different wt% (1, 2 and 3) of MgAl2O4 in situ composites was synthesized via ultrasonic cavitation by the addition of H3BO3 powders. Unreinforced alloy and composites were characterized to conclude the role of MgAl2O4 in modifying the wear behaviour of the composite. Worn-out samples and wear debris were examined by scanning electron microscopy and X-ray diffraction in order to obtain the major wear mechanisms of the developed composites. The addition of MgAl2O4 significantly reduces the wear rate of Al–4Mg alloy at higher loads. The operating wear mechanisms observed were delamination, oxidation, abrasion, adhesive, thermal softening and plastic deformation modes.

In the present work, Al-4 wt pct Cu/TiC composite was synthesized by the molten salt route that contains submicron-sized TiC particles in the Al-4 wt pct Cu matrix. The concentration of the TiC particle in the base alloy is 7.5 wt pct. Melt ultrasound treatment was done by remelting the as-cast composite at 1023 K (750 °C) in a view to refine the size of TiC particles to nanoscale and distribute them evenly in the matrix. The microstructure and age hardenability of the untreated and ultrasound-treated composites were investigated. The TiC particles accelerate the precipitation kinetics of CuAl2 phase in Al-4 wt pct Cu alloy. In the present study, the hardness obtained for untreated Al-4 wt pct Cu/TiC composite is 120 VHN within 5 hours of peak aging time, which is higher than the hardness of the monolithic Al-4 wt pct Cu, which is 104 VHN at 35 hours of peak aging time. Melt ultrasound treatment of Al-4 wt pct Cu/TiC composite shows no significant effect on the distribution and refinement of TiC particles in the matrix. However, it partially disintegrates the TiC into Al3Ti and Al4C3 particles. The ultrasound-treated composite showed an improved hardness of about 132 VHN at 5 hours of peak aging, in comparison to that of the untreated composite, by forming denser and homogeneous CuAl2 precipitates.

Al–4Mg/MgAl2O4 composites were successfully synthesized by the in situ reaction of Al–4Mg alloy melt and H3BO3 precursor in the presence of ultrasonic cavitation field. Ultrasonic-assisted synthesis facilitated generation of ~ 350-nm-sized MgAl2O4 particles. Enhanced reaction along with dispersion of MgAl2O4 was perceived due to the synergetic effect of ultrasonic cavitation. The presence of MgAl2O4 particles resulted in 3–4 times reduction in matrix alloy grain size, and the grain refinement was further enhanced by ultrasonic treatment. Compared to unreinforced alloy, ultrasonicated Al/MgAl2O4 composite exhibited an improvement in ultimate tensile strength by ~ 30 MPa with ~ 85% of ductility retention. Grain boundary strengthening, Orowan dispersion strengthening, coefficient of thermal expansion mismatch strengthening and load-bearing strengthening were the anticipated mechanism for enhancement in mechanical properties.

A novel approach was made for synthesis of in-situ MgAl2O4 particles in Al-4Mg alloy by addition of H3BO3 (0–2 wt%) precursor under Ultrasonic Treatment (UT). The synthesized composites were characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analysis. An improved reaction of H3BO3 with aluminium alloy was observed on 5 min UT. Increase in H3BO3 addition reduces the grain size of the aluminium alloy till 5–6 times although the ultrasonic effect further contributes greatly to the grain refinement by 2–3 times reduction additionally. Substantial grain refinement by UT was elucidated to the cavitation enhanced reaction of H3BO3 which resulted in the increased number density of MgAl2O4 particles. Enhanced wettability of the MgAl2O4 particles under UT makes it as potential heterogeneous nucleation sites of Al.

Mg–Zn–Sr alloys are suitable for biodegradable orthopaedic implants due to excellent biocompatibility and bone regeneration effect of Sr. For Sr additions exceeding 0.2 wt%, ternary phases are observed in the microstructure contrary to binary MgxZny and Mg17Sr2 intermetallics predicted by the existing phase diagrams and corrosion and mechanical properties reduce drastically. Thermal analysis employed for Mg–4Zn–xSr alloys (0 ≤ x≤2) recorded two peaks, hitherto unreported, at temperatures of ~ 514 and 409 °C with 2 wt%, and ~ 549 and 428 °C with 1 wt% of Sr added to Mg–4Zn alloy. In conjunction with SEM–EDAX and XRD analysis, one of these phases is identified as Mg11Zn4Sr3, with second one an unknown intermetallic (IM2). Formation of Mg17Sr2 phase is suppressed in the presence of Zn, and the ternary phase is favoured beyond the solid solubility of Sr in Mg. Solidification pathway of L → α-Mg + Mg11Zn4Sr3 + unknown intermetallic (IM2) has been proposed for the ternary compositions with Sr > 0.2 wt% investigated in the current study.

An attempt has been made to understand the microstructural evolution during semi-solid isothermal holding of liquidus cast Sr-modified A356 alloy. It was observed that the liquidus casting is effective in producing non-dendritic microstructure with average sphericity of 0.8 and 0.82 for unmodified and modified alloys, respectively. Isothermal holding of the samples at a temperature corresponding to solid fraction of 0.3 for 15 min enhanced the sphericity of unmodified and modified alloys to 0.84 and 0.85, respectively. Further increase in holding resulted grain coarsening and reduction in sphericity. The grain coarsening rate (K) of samples was analysed with Lifshitz–Slyozov–Wanger equation, and the values of K were found to be 58.3 and 98.3 µm3/s for unmodified and modified alloys, respectively. The grain coarsening in unmodified alloy was dominated by Ostwald ripening, whereas in case of modified alloy, grain coarsening was governed by grain coalescence.

Present study investigates the role of ultrasonic treatment (UT) on microstructure modification, porosity mitigation and their influence on mechanical properties of Sr modified A356 Al alloy. Addition of Sr in trace amount (500 ppm) to A356 alloy reduces the length of eutectic Si from 15.6 µm to 0.65 µm with a concomitant increase in porosity from 0.84% to 3.59%. Ultrasonic treatment of Sr modified A356 Al alloy retains the modification of eutectic Si (0.57 µm) and reduces the specific porosity volume to 0.86%. The effect of microstructure modification and porosity mitigation reflects on the mechanical properties of A356 Al alloy. While the Sr addition to A356 alloy reduces the tensile properties, UT of the Sr added alloy results in improved tensile properties. The mechanism of microstructure modification, porosity formation and UT assisted porosity mitigation are discussed in detail. Ultrasonic cavitation assisted degasification and bi-film breakage is proposed as the governing mechanism for porosity alleviation.

In the present study, Gas Tungsten Arc Welding (GTAW) of Inconel 718 alloy has been carried out at different welding currents with and without ultrasonic vibration. In the absence of ultrasonic treatment, samples welded with a current of 80 A have shown a crack length of 15 mm which is found to increase to 35 mm for a welding current of 120 A. The slow solidification rate associated with high welding current causes increase in hot cracking length. Non-equilibrium Scheil solidification simulation of Inconel 718 based on CALPHAD approach suggests that the long freezing range of more than 175 °C, small fraction of eutectic, i.e., less than 10% in susceptible freezing range (SFR) and segregation of low melting point Laves and γ′′ (Ni3Nb) phases play critical roles in hot cracking behavior of Inconel 718 alloy. Ultrasonic treatment during solidification of weld metal has decreased the crack sensitivity and dendritic arm length of Inconel 718 alloy from 47.5% to 13.3% for the welding current of 120 A. There was a corresponding reduction in dendritic arm length from 1256 to 89 μm. Further, it was observed that the welding current has very limited role in the hot cracking behavior of Inconel 718 alloy in the presence of ultrasonic vibration. Dendritic fragmentation, grain refinement and reduction in solute segregation are recognized as the main factors that mitigate hot cracking tendency of Inconel 718 alloy by ultrasonic vibration.

AA7075/TiB2 composites have been synthesized through both in situ salt-melt reaction method and ultrasound assisted in situ process. Microstructural studies reveals that ultrasound assisted in situ method improves the dispersion of TiB2 particles and reduces the porosity level. Moreover, the ultrasonic treatment refines the reinforcement particle size along with improvement in particle dispersion. The mechanical property assessment confirms that ultrasonic treatment improves the mechanical properties of composite. The hardness of the AA7075 alloy is increased from 55 HV to 74 HV by the addition of 5% TiB2 particles and it further increased to 82 HV by ultrasonic treatment. A similar trend is also observed when weight percentage of particles increases to 7.5%. Addition of 5% in situ TiB2 particles increases the ultimate tensile strength of AA7075 alloy by 60 MPa and it is further enhanced by 80 MPa upon ultrasound assisted process. Composites have shown a small reduction in ductility when compared to un-reinforced alloy, though 81% ductility of matrix alloy has been retained. Similar trend has been observed in composites fabricated using ultrasonic assisted casting.

In this study, the foaming behavior of metal matrix composites (MMCs) containing micron- and nano-sized TiB2 particles was compared. Foaming was achieved by adding blowing agent into the MMC melt at 670 °C. Macrostructural and microstructural characterization of the foams were performed by using X-ray tomography and scanning electron microscopy. Quasi-static compression tests were conducted to analyze the mechanical behavior of the foams. Foams stabilized by nanoparticles showed higher expansion than those stabilized by micron-sized particles indicating a better stabilization by nanoparticles. The foams containing nanoparticles also exhibited better mechanical properties. This is mainly due to the presence of nanoparticles in the microstructure.

Phase diagram of Mg-Sn-Y ternary alloy systems were constructed thermodynamically using calculation of phase diagram (CALPHAD) approach. The thermodynamically calculated isothermal section of Mg-Sn-Y ternary alloy at 400 °C was validated by comparing with results reported in the literature and few selected key experiments. The calculated results matched well with the experimental results. Vertical section phase diagram of Mg-1Sn-xY and Mg-3Sn-xY alloys were constructed on the basis of solidification analysis and compared with thermodynamically calculated phase diagram. The thermodynamically calculated liquidus temperature for Mg-1Sn-xY system matched well with the experimental results. However, significant differences in solidus temperature and solubility limit were observed for Mg-1Sn-xY alloys. This difference is attributed to the shift in composition and temperature for L→L+α-Mg + Sn 3 Y 5 and L→α-Mg + Sn 3 Y 5 +Mg 24 Y 5 phase transformations. In Mg-3Sn-xY phase diagram, a gradual decrease in liquidus temperature is experimentally observed up to 13 wt % Y and further addition of Y leads to increase in liquidus temperature. The increase in liquidus temperature is attributed to the formation of MgSnY intermetallic compound which is not predicted by thermodynamic model. The lack of experimental data on the enthalpy of formation of ternary MgSnY compound is one of the major reasons for the discrepancy between the thermodynamic calculation and experimental results.

This paper investigates the effect of microstructure modification by heat treatment on stress corrosion cracking (SCC) behavior of Mg 4Zn alloy in simulated body fluid (SBF). Mg 4Zn alloy in as cast, solution heat treated and peak aged conditions was susceptible to SCC in SBF when strained at 3.6 × 10−6 s−1. SCC index based on fracture energy is least for solutionized alloy (0.84), while 0.88 for as cast and peak aged alloys. Fractographic analysis indicates predominantly intergranular SCC for solution treated alloy initiated by anodic dissolution near grain boundaries. As cast and peak aged alloy shows mainly transgranular failure due to hydrogen embrittlement adjacent to secondary phase particles.

The present study deals with the effect of Ultrasonic Treatment (UT) on the synthesis, characterization, and mechanical properties of Al-4.4 wt% Cu alloy reinforced with 2 vol % of Graphite (Grp) particles. Microstructural analysis of composite confirms that the UT enhances the wettability, de-agglomeration, and uniform distribution of Grp particles in the matrix. The micron-sized Grp has been flaked off to submicron particles with increase in aspect ratio from ∼4.7 to ∼6.5 due to ultrasonic cavitation effect. In comparison with monolithic Al-4.4 wt % Cu alloy an overall grain size reduction of 74% has been observed in composite with UT. Grp particles’ reinforcement together with grain refinement has improved the mechanical properties viz. hardness, compressive strength and tensile strength of the synthesized composite with UT. The strengthening mechanisms of the Grp particles in the synthesized composites have been analyzed and discussed.