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A disordered atomic layer instead of traditional intermetallic compounds is formed in the bonding interface of ceramic and metal in the metallization of ceramics under ultrasonication. A deep understanding of the bonding mechanism between poor-wetted ceramics and low-temperature metals remains limited with regard to high metallization efficiency and nanoscale bonding structure. In this work, the metallization of AlN and TiN ceramics was realized using Sn9Zn metal with the aid of ultrasonication. The microstructure, energy, and element sources of the ceramic/metal interface were analyzed. Results show that a nanoscale amorphous layer is formed between the ceramics and the metal, and this layer can bond easily with AlN or TiN and Sn9Zn because of the irregular arrangement of its atoms. Some dispersed nanocrystals are also present in the amorphous bonding layer. The thermal effect of ultrasonic cavitation produces a high temperature above 106 K, which provides the energy for the bonding of AlN or TiN with Sn9Zn. O and Zn accumulate in the Sn-9Zn/AlN bonding layer. Zn originates from Sn9Zn. O could be from the O2dissolved in the liquid solder or the O2adhering to the ceramic. A small amount of AlN decomposes because of its high ΔG of decomposition. However, TiN decomposes into Ti and N2under the extreme condition caused by ultrasonic cavitation. The accumulated Ti in the Sn-9Zn/TiN bonding layer originates from TiN. The source of the accumulated O is the same as that of Sn-9Zn/AlN bonding layer.

The breaking of surface oxide film in a technology area of ultrasonic-assisted diffusion joining manufacturing of large-size structure components is a challenge. In this work, a novel method of breaking surface oxide film of Al alloys based on first diffusion-migrating and then suspension-broken was investigated. Diffusion bonding of 6063Al alloys was performed by Zn interlayer at temperature below 400 °C. The oxide film migrated away from the Al alloy base metal by solid phase diffusion at 360 °C, and remained in the joint as a nanoscale oxide film. When temperature increased to 390 °C, the oxide film suspended in the Zn–Al eutectic liquid phase were rapidly broken up into small fragments through an instantaneous ultrasonic action (only 0.3 s). The change of acoustic pressure in the liquid metal proved that the suspended continuous oxide film was broken by the micro-jet acted simultaneously on both sides of oxide film induced by the ultrasonic cavitation effect. Finally, the inter-diffusion between Zn and Al at 360 °C was promoted by a longer holding time to obtain the homogeneous joint composed by Zn–Al eutectoid phase containing oxide fragments, and had a higher strength than the base metal. The breaking of oxide film and joint homogenization were performed under pressure-less condition, which effectively avoided the squeezed-out of the liquid phase. This technology shows a great potential for manufacturing large-size joint of industrial products.

The success of deep neural networks and their potential use in many safety-critical applications has motivated research on formal verification of deep neural networks. A fundamental primitive enabling the formal analysis of neural networks is the output range analysis. Existing approaches on output range analysis either focus on some simple activation functions, such as $\text{relu,}$ or compute a relaxed result for some activation functions, such as exponential linear unit $\text{({elu}}$). In this article, we propose an approach to compute the output range for feed-forward deep neural networks via linear programming. The key idea is to encode the activation functions, such as $\text{{elu}}$ and $\text{sigmoid}$, as linear constraints in term of the line between the left and right end-points of the input range and the tangent lines on some special points in the input range. A strategy to partition the network to get a tighter range is presented. The experimental results show that our approach gets a tighter result than RobustVerifier on $\text{{elu}}$ networks and $\text{sigmoid}$ networks. Moreover, our approach performs better than (the linear encodings implemented in) Crown on $\text{{elu}}$ networks with $\alpha =0.5, 1.0$ and $\text{sigmoid}$ networks, and better than CNN-Cert and DeepCert on $\text{{elu}}$ networks with $\alpha = 0.5$ or 1.0. For $\text{{elu}}$ networks with $\alpha = 2.0$, our approach can achieve results that are closed to Crown, CNN-Cert, and DeepCert. Finally, we also found that the network partition helps to achieve a tighter result as well as to improve the efficiency for $\text{{elu}}$ networks.

• Diffusion bonding of Al alloy retaining continuous oxide layers were successfully achieved in air by a low-temperature and low-pressure diffusion bonding mothed using a Zn interlayer. • The dynamic behaviors of the oxide layers include the cracking phenomenon, the "subcutaneous diffusion" and migration behavior were found during diffusion bonding. • The essence of migration behavior of oxide layers is that a relative displacement in space with the consumption of Zn, showing a movement toward the center of the joint. The oxide layer on the surface has always been a key obstacle to achieving the diffusion bonding of Al alloys. It is a challenge for performing diffusion bonding without removing oxide layers. Herein, diffusion bonding of Al alloy retaining continuous oxide layers was successfully achieved in the air by a low-temperature and low-pressure diffusion bonding mothed using a Zn interlayer. During the bonding processes, conducted at 360 °C and 3 MPa, Zn diffused into Al through cracks of thin oxide layers to form the joint composed Al/(diffusion layer)/(oxide layer)/(Zn)/(oxide layer)/(diffusion layer)/Al. The diffusion layers were composed of Zn-Al eutectoid, and the oxide layer included nanocrystals and amorphous Al 2 O 3. The shear strength of joints containing continuous oxide layers was about 30 MPa. Interestingly, the migration behavior toward the joint center of the interfacial oxide layers was observed with consuming of the Zn interlayer. The cracking phenomenon, the "subcutaneous diffusion" and the migration behavior of oxide layers were verified and analyzed by the diffusion bonding of anodized 6063Al-6063Al. Subsequently, the dynamic migration mechanism of oxide layers with elements diffusion and bonding interface strengths were discussed in detail. The ability to join Al alloys in the air at low temperatures and low pressure suggests a highly practical and economic method for diffusion bonding. [Display omitted] [ABSTRACT FROM AUTHOR]

We used ultrasonic-assisted brazing to join Al-Si-coated Ti alloys and Al alloys with a Zn-Al-Si filler metal. At the interface between the Ti alloy and Al-0.1Si alloy coating, a block TiAl3phase formed. In contrast, for the Al-5Si alloy coating, the interfacial reaction layer of the joint consisted of a block Ti(Al,Si)3phase and needle-like Ti7Al5Si12phase. Finally, a granular Ti7Al5Si12phase was formed at the joint interface for the Al-12Si alloy coating. The tensile strength of the joints formed with the Al-0.1Si and Al-12Si alloy coatings was only 160 -185 MPa, and cracks propagated mainly through the reaction layer. The tensile strength of the joints formed with the Al-5Si alloy coating ranged from 210 to 215 MPa, and cracks appeared entirely within the coating, subsequently expanding along the coating and ultimately resulting in failure of the joint.

We used ultrasonic-assisted brazing to join Al-Si-coated Ti alloys and Al alloys with a Zn-Al-Si filler metal. At the interface between the Ti alloy and Al-0.1Si alloy coating, a block TiAl3phase formed. In contrast, for the Al-5Si alloy coating, the interfacial reaction layer of the joint consisted of a block Ti(Al,Si)3phase and needle-like Ti7Al5Si12phase. Finally, a granular Ti7Al5Si12phase was formed at the joint interface for the Al-12Si alloy coating. The tensile strength of the joints formed with the Al-0.1Si and Al-12Si alloy coatings was only 160 -185 MPa, and cracks propagated mainly through the reaction layer. The tensile strength of the joints formed with the Al-5Si alloy coating ranged from 210 to 215 MPa, and cracks appeared entirely within the coating, subsequently expanding along the coating and ultimately resulting in failure of the joint.

AZ31B Mg alloys were joined with a pure Zn interlayer via ultrasonic-assisted transient liquid phase bonding. The formation and evolution of intermetallic compounds (IMCs) and the mechanical properties of the bonded joints were investigated. Results showed that joints could form within an extra short time of 0.1 s via eutectic reaction, eutectoid reaction and diffusion bonding. Mg-Zn eutectoid structures, IMCs of MgZn and MgZn2formed inside the bonded joint. The width of the MgZn2phase decreased with prolonged ultrasonication time, high ultrasonication power, and sonotrode pressure. The entire joint was characterized by eutectoid structures without MgZn2at a high sonotrode pressure of 0.4 MPa. MgZn2had a higher hardness and modulus than MgZn, Mg-Zn eutectoid structure, and Mg substrate. Joints fractured through the MgZn2phase and eutectoid structure had shear strength values of 30 and 40 MPa, respectively.

ABSTRACTAn ultrasonic-assisted semi-solid brazing method was used to control Mg/Al intermetallic compounds (IMCs). Zn–20.95Al, which has a large semi-solid temperature range of 60°C, was chosen as filler metal. Oxide films on the Al/Mg surfaces were removed despite the semi-solid state of the filler metal at 430°C. Al–Mg–Zn IMCs were observed inside the joint at 667 W and 5 s. The IMCs was reduced as ultrasonication time was prolonged. At high power of 1000 W, short ultrasonication time was needed to guarantee that no IMCs remained inside the joint. Otherwise, new IMCs formed because of serious cavitation erosion on substrates. Ultrasonication time of 20 s was unable to completely eliminate IMCs and solid phases at 423°C.

An ultrasonic-assisted semi-solid brazing method was used to control Mg/Al intermetallic compounds (IMCs). Zn–20.95Al, which has a large semi-solid temperature range of 60°C, was chosen as filler metal. Oxide films on the Al/Mg surfaces were removed despite the semi-solid state of the filler metal at 430°C. Al–Mg–Zn IMCs were observed inside the joint at 667 W and 5 s. The IMCs was reduced as ultrasonication time was prolonged. At high power of 1000 W, short ultrasonication time was needed to guarantee that no IMCs remained inside the joint. Otherwise, new IMCs formed because of serious cavitation erosion on substrates. Ultrasonication time of 20 s was unable to completely eliminate IMCs and solid phases at 423°C.

The joining of an aluminium matrix composite to a titanium alloy by ultrasonic-assisted brazing using a Zn-based filler metal was investigated. An approximately 50-nm-thick amorphous Zn–Mg–Si interfacial layer formed between the Zn-based filler metal and SiC particles adjacent to the Ti alloy side of the brazed joint. Many of the Zn crystals that formed during brazing nucleated in this amorphous layer, suggesting that the amorphous layer acted as a diffusion layer between the Zn-based filler metal and SiC ceramic during brazing. This work not only explains the improvement in the performance of the brazing joints by the ultrasonic action but also proposes a strategy to optimise the interfacial structure for other metallic alloys.

ABSTRACTIn this work, friction spot welding (FSpW) was used to weld dissimilar 6063/5083 aluminium alloys, and the effects of the sleeve plunging speed on joint microstructures and the lap shear properties were discussed. Results showed that the keyhole can be eliminated using FSpW. Bending hooks changed to a flat morphology when the plunging speed was increased. Excellent bonding was formed at the lap interface in the sleeve-affected zone. As the sleeve plunging speed was increased from 40 to 110 mm min−1, the lap shear failure loads for the joints first increased and then decreased. A maximum failure load of 8017 N was attained when using a sleeve plunging speed of 80 mm min−1. All joints fractured at the lap interface.

In this work, friction spot welding (FSpW) was used to weld dissimilar 6063/5083 aluminium alloys, and the effects of the sleeve plunging speed on joint microstructures and the lap shear properties were discussed. Results showed that the keyhole can be eliminated using FSpW. Bending hooks changed to a flat morphology when the plunging speed was increased. Excellent bonding was formed at the lap interface in the sleeve-affected zone. As the sleeve plunging speed was increased from 40 to 110 mm min-1, the lap shear failure loads for the joints first increased and then decreased. A maximum failure load of 8017 N was attained when using a sleeve plunging speed of 80 mm min-1. All joints fractured at the lap interface.

A high strength joint obtained at relatively low temperature and pressure by diffusion bonding has always been a challenge for manufacturing of aluminum alloy heat sinks. In this work, joining of 6063Al alloys was performed by a novel liquid and solid phase diffusion bonding method with an Zn–30Sn hypereutectic interlayer. It was achieved at a heating temperature of 360 °C and a pressure of 1 MPa. A 6063Al joint bonded was composed mainly of Zn–Al eutectoid phases and had a higher strength than the base metal. During the diffusion bonding process, the joint was constituted of Sn–Zn eutectic phases and η-Zn phases at initial diffusion stage. The proportion of Sn–Zn eutectic phases gradually decreased and Zn–Al eutectoid phases increased in a joint through inter-diffusion between base metal and interlayer with increasing of holding time. The η-Zn phases finally transformed into Zn–Al eutectoid phases with depleting of Sn–Zn eutectic phases, in which only 0.02 wt% Sn element was remained in the joint. The liquid and solid phase diffusion mechanisms were revealed. The penetration of Sn to the grain boundary of Al alloy happened under an assistance of the Zn diffusion. The Al originated from base metal diffused into η-Zn phases, forming Zn–Al eutectoid phases.

This paper focuses on the process of ultrasonically assisted induction brazing with regard to titanium brazing. The titanium alloy TiAl6V4 was brazed using an aluminum-based filler alloy (AlMg2.5Cr0.3). It was apparent that the layer thickness of the brazing foil as well as the brazing temperature and the intensity of the ultrasound are significant influencing factors of the combined brazing process and microstructure. It is the aim of this paper to draw conclusions from the microstructural and mechanical investigations of the brazed joint about the process parameters, which are crucial for the properties and quality of the joint. The evaluation of the microstructure of the joint was conducted by means of metallographic investigations and results obtained by means of scanning electron microscopy. Besides mechanical microhardness measurements, strength investigations were conducted in order to evaluate the quality of the joint. Furthermore, the results of conventional vacuum brazing processes were correlated in order to be able to better facilitate and understand the adapted induction brazing process.

In this work, ultrasonic-assisted transient liquid bonding (UATLP) was used to rapidly join dissimilar Al/Mg alloys in the air. The pure Zn interlayer was chosen to preventing Al–Mg intermetallic compounds (IMCs). The effects of the bonding time on the microstructure and mechanical properties of the joints were studied. The joint formation mechanism was analyzed. Results show that the Al–Mg IMCs can be avoided when the ultrasonic time was shorter than 3 s. The oxide layer on the Al substrate was incompletely removed when the ultrasonic time was shorter than 2 s, and the joint was characterized by Mg–Zn eutectic, MgZn, and MgZn2from the Mg side to the Al side. The joint had a shear strength of 16 MPa and failed through the MgZn2/Al interface under such condition. The oxide layer on the Al substrate was removed when the ultrasonic time was increased to 3 s. The joint had a shear strength of 24 MPa, and it failed through the MgZn2layer and the Mg–Zn eutectic. The entire Zn foil interacted with the Mg and Al substrate at a prolonged ultrasonic time of 6 s. Al–Mg IMCs of Al3Mg2and Al12Mg17appeared because a large amount of Al and Mg atoms diffused into the joint. The joint strength decreased to 11 MPa and failed through the Al3Mg2layer.

•Acoustic intensity in the liquid solder remarkably affects the microstructure and mechanical properties of the soldered joints.•High acoustic intensity was produced by applying a small lap width without increasing input ultrasonic power.•The melting point of Zn increased by 73.8 °C under the high pressure caused by bubble collapse according to the Clausius–Clapeyron equation.•Zn grains were significantly refined due to undercooling-induced direct solidification caused by cavitation.•Shear strength and hardness respectively increased by 24% and 17% when lap clearance decreased by 50%.