Effect of rapid thermal shock cycle on the thermomechanical reliability of 20Sn-80Pb solder bumps

The influence of rapid thermal shock(RTS) cycles on 20Sn-80Pb solder bumps was studied. In the study, 20Sn-80Pb solder bumps were prepared by desktop nitrogen lead-free reflow soldering machine. The prepared 20Sn-80Pb solder bumps were used for RTS test in the temperature rang of 0°C ~ 150°C. One cycle of RTS is 24 seconds, and the temperature rise and fall rate of RTS is 12.5 C/s. The result indicated that when the cycle of RTS reached 1500T (here T is cycle, the same below), the shear strength of Sn-80Pb solder bump dropped by drastically 48.6%. Whereas, when the cycle of RTS reached 5500T, 20Sn-80Pb solder bumps’ shear strength decreased to 18.35 MPa, which increased by 7.5% compared with that of l6.97 MPa at 4500T. With the increase of RTS cycles, 20Sn-80Pb solder bumps’ shear strength was a decreasing trend and the fracture mechanism changed from ductile fracture to ductile-brittle mixed fracture, which could be subject to the thickening of the interfaical IMCs and the stress concentration caused by the growth of interfacial IMCs. To understand the changes of the mechanical properties of 20Sn-80Pb solder bumps, the influences of RTS on the crack and interfacial IMC of 20Sn-80Pb solder bumps were studied in details.

Effect of Transverse Magnetic Field On Microstructure And Mechanical Properties of Ti-6Al-4V Manufactured By Laser-MIG Hybrid Welding

In this paper, the external transverse magnetic field is used to assist the laser-MIG hybrid welding for Ti-6Al-4V (TC4). The microstructure and mechanical properties such as microhardness and tensile properties of the weld joints under 24 mT external magnetic field (EMF) and the referring weld joint without EMF are investigated and discussed. Results show that transfer layer (TL) performs the lowest microhardness in the weld seam and tensile specimens fail in this area for the referring weld joint without EMF, which indicates the TL is the weakest zone in the weld seam. The mechanical properties of weld seam improve significantly under 24 mT EMF, which average microhardness in TL increases 9.3% and failure stress of tensile specimens improve by 16.7%, whilst a mixed fracture mode is operative in the fracture surfaces. The research reveals the elementary microstructure of TC4 laser-MIG hybrid welding is in correlation to welding heat input under the influence of EMF.

Effect of CeO2 Content on Microstructure and Properties of SiCp/Al-Si Composites Prepared by Powder Metallurgy

The effect of CeO2 content on the microstructure and properties of SiCp/Al-Si composites prepared by powder metallurgy was studied, and the mechanism of CeO2 in composites was deeply analyzed. The results show that the addition of the appropriate amount of CeO2 can refine the Si particles and improve the tensile properties of the SiCp/Al-Si composites. As the CeO2 content increases from 0 to 0.4 vol%, the particle size of the Si phase shows a tendency to decrease first and then increase, while the tensile strength, yield strength, and elongation of the composites show a trend of first increasing and then decreasing. When the CeO2 content is 0.2 vol%, the refining effect of CeO2 and the tensile properties of composites are the best. The fracture mode of SiCp/Al-Si composites with a rare earth addition is a mixed fracture. There are three main mechanisms for CeO2 in SiCp/Al-Si composites. One is when CeO2 serves as the nucleation substrate of Si phase to refine Si particles. The second is when CeO2 reacts with the alloying elements in the aluminum matrix to form a new phase, CeCu2Si2, which can not only play a role of dispersion strengthening, but also improve the bonding strength between Al matrix and Si particles. The third is the pinning effect of CeO2 and CeCu2Si2 particles on grain boundaries or phase boundaries to refine aluminum grains.

Comparative evaluation of bond strength of three self-adhering flowable composites to sound and demineralized enamel – An in vitro study

Objectives: The purpose of this study was to determine bond strength of three self-adhering flowable composites. Materials and Methods: Mean tensile bond strength was measured in three groups – Group A – Constic, Group B – Dyad Flow, and Group C – Fusio Liquid Dentin on sound and demineralized primary teeth. Fracture pattern was studied using a stereomicroscope for each sample and in classified as adhesive, cohesive, or mixed fracture. Results: Mean tensile bond strength in sound enamel of Group A (Constic) was found to be 10.79 + 4.24, Group B (Dyad Flow) was 10.30 + 4.63, and of Group C (Fusio Liquid Dentine) was 11.87 + 4.45. No significant difference was found between the three groups (f = 0.327 and P = 0.724). However, a significant difference was found with demineralized enamel in three groups. Constic and Dyad Flow exhibited adhesive fracture pattern in majority of samples on sound enamel, whereas Fusio Liquid Dentin had mixed fracture pattern. On demineralized enamel, Constic exhibited adhesive fracture pattern majorly, whereas Dyad flow demonstrated mixed pattern and Fusio Liquid Dentin had more of cohesive fractures. Conclusion: Constic, Dyad Flow, and Fusio Liquid Dentin can be used instead of conventional pit and fissure sealants or in small occlusal cavities in primary teeth as a single step material.

Experimental and Numerical Study on Fracture Characteristics of Interface between In Situ Engineered Cementitious Composites and Steel Deck

In this study, engineered cementitious composite (ECC) is used as the pavement of orthotropic steel deck bridge and an epoxy adhesive is used to achieve wet-bonding between the steel deck and cast-in-place ECC. To investigate the fracture properties of bimaterial interface, the double cantilever beam (DCB) and 4-point end notched flexure (4ENF) specimens were used to obtain the fracture toughness, and virtual crack closure technology (VCCT) was used to calculate the energy release rates. A mixed fracture criterion was also established based on the blister test in this study. In addition, for the phenomena of water accumulation in the interface cracks, the hydrodynamic pressure under load was evaluated with a two-way fluid-solid coupling model and the propagation mechanism of cracks at the water-bearing interface was explored. The results showed that the energy release rates at the crack front showed obvious nonuniform distribution characteristics. The blister test indicated that a mixed fracture was in good agreement with the linear fracture criterion. The fracture effect produced by the hydrodynamic pressure of the interfacial water-bearing crack was far less than the fracture toughness of the interface, which indicated that the hydrodynamic pressure could hardly destroy the interface at one time but might cause the erosion fatigue damage of the interface.

Microstructure and Properties of Ultrasonic Assisted Sn2.5Ag0.7Cu0.1RExNi/Cu Solder Joint S Under Thermal Cycling

Through ultrasonic wave assisted Sn2.5Ag0.7Cu0.1RExNi/Cu(x=0, 0.05, 0.1) soldering test and -40~125℃ thermal shock test, the microstructure and mechanical properties of Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints under thermal cycling were studied by the SEM, EDS andXRD. The results show that the Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints with high quality and high reliability can be obtained by ultrasonic assistance. During the thermal cycling process, the shear strength of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints had a linear relationship with the thickness of interfacial intermetallic compound (IMC). The addition of an appropriate amount of Ni could inhibit the excessive growth of IMC, improve the shear strength of solder joints and improve the reliability of solder joints. Under the condition of 1000 cycles of thermal cycling, the thickness and roughness of IMC of the solder joints with 0.05 wt.% Ni were the smallest, and the shear strength of the solder joints was 19.8 MPa, which was 28.6% higher than that of the solder joints without Ni.The interfacial IMC layer of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints consisted of (Cu,Ni) 6Sn5 and Cu3Sn. In the thermal cycling, the thickness of interfacial IMC of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints was linearly related to the square root of equivalent time. The growth of interfacial IMC of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints had an incubation period, and the growth of IMC was slow within 300 cycles. And after 300 cycles, the IMC grew rapidly, the granular IMC began to merge, the thickness and roughness of IMC increased obviously, the defects such as microcracks and microvoids began to appear, and the shear strength of the solder joints decreased rapidly.The fracture mechanism of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints changed from the ductile-brittle mixed fracture in the solder/IMC transition zone to the brittle fracture in the interfacial IMC.

Effect of the upset pressure on Microstructure and Properties of Friction Welded Joints of 6082 aluminum alloy/304 stainless steel

The dissimilar connection between 6082 aluminum alloy and 304 stainless steel was realized by continuous drive friction welding. Microstructures of the joint were studied by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffractometry (XRD). In the process of continuous drive welding, the intermetallic compounds (IMCs) Fe2Al5 phase was observed at the interface, the formation mechanism of IMC was discussed, and the corresponding analysis model was established. When the upset pressure in the range of 6–10 MPa, the element diffusion distance increases with the increase of upset pressure. The tensile strength of the joint increased firstly and then decreased with the increase of upset pressure. The joint’s maximum tensile strength can reach 234 MPa, and tensile fracture of the joint exhibited brittle-tough mixed fracture characteristics.

Microstructure and Mechanical Properties of Tungsten Inert Gas Weld Joints of Sprayed and Cast Aluminium–Lithium Alloy

The weld joints of sprayed 2195-T6 and cast 2195-T8 aluminium–lithium alloy were created using tungsten inert gas with filler wire. The microstructures and mechanical properties of the weld joints were examined. The results of the microstructure analysis showed that the width of the equiaxed grain zone (EQZ) and the amount of the second phase θ’(Al2Cu) was greater in the weld joint of the cast 2195-T8 Al–Li alloy than that of the sprayed 2195-T6 Al–Li alloy. Tensile testing indicated that failures occurred in the EQZ and partially melted zone (PMZ) for both weld joints. The tensile strength and elongation of the weld joints of the sprayed 2195-T6 and cast 2195-T8 Al–Li alloys were about 68.2%, 89.7%, and 50.7% and 28.3% those of the base metal in the joint, respectively. The cast 2195-T8 Al–Li alloy joint had more pores and cracks, resulting in lower tensile strength and elongation than those in the sprayed alloy. Further, the tensile fracture surface morphology indicated that the fracture mode of the sprayed 2195-T6 Al–Li alloy was a mixed fracture mode dominated by plastic fracture and that of the cast 2195-T8 Al–Li alloy joints was a mixed fracture mode dominated by brittle fracture.

Effect of Heat Treatment on Microstructure and Mechanical Properties of As-Forged ZYK530 Mg Alloy

In the paper, the microstructure and mechanical properties of ZYK530 Mg alloy with different aging heat treatment processes were analyzed and studied by OM, SEM, EDS and XRD. The results show that after heat treatment at different temperatures and aging times, the hardness of the alloy first decreases, then increases in a wave-like manner, and then decreases in a wave-like manner after reaching its peak value. The optimum aging process of ZYK530 alloy is T5-220°C×5h, and the maximum hardness is 88.34HRE, which tensile strength, yield strength and elongation are 335MPa, 305MPa and 13.5% respectively. Compared with the untreated forged alloy, the mechanical properties are increased by 6.3%, 4.8% and 35%, which its fracture mechanism is mainly ductile-brittle mixed fracture.