Study Of The Interface And Properties Of Palladium-clad Aluminum Composite Wires

With the development of manned space engineering,as the heart of large aircraft and manned space rocket,rocket engine is particularly important.Solid rocket motor has been paid more and more attention by scientists because of its simple structure and low cost.Pd/Al composite wire is an excellent ignition material for solid rocket motor,which meets the requirements of short ignition response time,small ignition peak,easy control of ignition time and simultaneous ignition of propellant column combustion surface in the engine.In this paper,Pd/Al composite wires with φ0.10mm were prepared.The effects of different annealing temperatures on the interface and macroscopic properties of Pd/Al composite wires were studied.The effects of different currents on the interface and macroscopic properties of Pd/Al composite wires were studied by means of constant current.The heat release and fusing products of Pd/Al composite wires at different annealing temperatures were studied.It provides theoretical data support for the development of Pd/Al composite wires with better performance.The growth of intermetallic compounds at the interface of Pd/Al composite wires increases with the increase of current intensity.The intermetallic compound at Pd/Al interface under 1A and 4A current is Al3Pd2 phase,and the intermetallic compound at the interface under 2A and 3 A is Al21Pd8 phase.The Joule heat generated during electrification not only speeds up the annealing and recrystallization process,but also accelerates the diffusion and growth of the interfacial layer.As a result,the conductivity and elongation of Pd/Al composite wire have no obvious change,but the tensile strength decreases slightly.When the constant current time of 3 A is 1 s,the tensile strength,elongation and conductivity are the lowest,which are 162.65 MPa,1.08%and 48.48%IACS.At the early stage of annealing at 200℃-300℃,as diffusion proceeds and the atomic concentration of the AlPd phase is reached,the A13Pd2 phase is formed first at the interface instead of the AlPd phase due to the close concentration of the AlPd phase and the lower effective formation energy of the Al3Pd2 phase.At 350℃ annealing for 5 s,the temperature is higher,the interface diffusion speed is accelerated,the Al and Pd interface is fully contacted,reaction diffusion occurs,the instantaneous heat release is larger to reach a higher temperature,producing Al3Pd5 phase;200℃ annealing for 3600 s and 10800 s intermetallic compound at the interface is Al3Pd2 phase and Al21Pd8 phase;250℃ annealing for 900 s intermetallic compound at the interface is Al3Pd2 phase and Al21Pd8 phase;250℃ annealing for 900 s intermetallic compound at the interface is Al3Pd2 phase and Al21Pd8 phase,annealed at 10800 s is the Al3Pd2 phase and the Al21Pd8 phase;annealed at 300℃ for 120 s and 10800 s the intermetallic compound at the interface is the Al3Pd2 phase;annealed at 350℃ for 120 s is the Al3Pd2 phase and the Al21Pd8 phase,annealed at 10800 s is the Al3Pd2 phase.The microstructure of the annealed Pd/Al composite wire was observed and it was found that the thickness of the intermetallic compound layer at the interface increased with increasing annealing temperature and time;when the thickness of the interface layer is thin,the presence of the intermetallic compound had less influence on the properties such as elongation and electrical conductivity,and the intermetallic compound played a role in coordinating the deformation between Pd and Al,so that Pd and Al would not separate during the tensile process,which improved the interfacial bond strength;an increase in the thickness of the interface layer would reduce the tensile fracture properties of the Pd/Al composite wire.Different intermetallic compounds at the interface of Pd/Al composite wire have some effects on the discharge heat.When there are Al3Pd2 and Al21Pd8 phases,the discharge heat of Pd/Al composite wire is high,and the presence of AlPd phase will reduce the subsequent discharge heat.Al3Pd2 phase and Al21Pd8 phase were also found in current fusing products,but no AlPd phase was observed.The current ignition of Pd/Al composite wire mainly relies on the generation of Al3Pd2 and Al21Pd8 phases at the interface.