| SiCp/Al composites with high volume fraction are widely used in aerospace,automotive and electronic components,especially in electronic packaging.Therefore,it is very important to study the proper bonding methods of SiCp/Al composites.However,because these materials contain a large number of reinforced SiC particles,the wettability of substrate surface is poor,it is difficult to achieve the bonding of the composites.In this paper.Al/Ni nanomultilayers were used as the heat source to join high volume fraction of SiCp/Al composites.The effects of the parameters on the welded joints were investigated.The ideal welding joints were obtained.The exothermic peak of the nanomultilayers can be measured by DSC.and the self-propagating reaction can occur when the temperature is above 200℃.According to the properties of nanomultilayers,the heating rate is not less than 200℃/min,otherwise self-propagating reaction capability was lost.Before the experiments,the ANSYS finite element simulation software was used to simulate the welding temperature field.The results were shown that the thickness of nanomultilayers should be no less than 120μm and the cooling rate reached 500℃/ms.The heat affected zone of Al/Ni nanomultilayers as the heat source is only 0.5mm in the thickness direction.The heat release increased with the thickness of Al/Ni nanomultilayers.According to the results of the ANSYS simulation,the experiments were carried out by appropriate thickness of Al/Ni nanomultilayers.When Al/Ni nanomultilayers were as heat resource,the thickness was 180μm,and slice Al-Si-Mg brazing fillers were used in self-propagating joining,the joints were composed of substrate,fillers and self-propagation products AlNi intermetallic compounds,and the joint strength is 32.8MPa under the pressure of 120MPa.With the increase of pressure,the joint strength decreased,and cracks were appeared in the substrate.Under the same test conditions,Al-Si fillers were used,the maximum joint strength is 23.8MPa,and the fillers were not spread uniformly in joint interface,and there were gaps and holes and other defects.When the thickness of Al/Ni nanomultilayers was 120μm,and slice Al-Si-Mg fillers and slice Al-Si fillers were used in self-propagating joining,the joint condition was mainly determined by the test pressure.Under the proper pressure,the fillers and interface of the joint are wetted well,but there was still a large gap in the interface,which seriously affects the quality of welded joints.The hardness of the joint presents a "hard-soft-hard-soft-hard" mechanical non-uniform state.The results of XRD showed that the interface was composed of Al,SiC phase.It was found that the welding pressure and the thickness of the nanomultilayers are important parameters in the experiments.The thickness of the nanomultilayer film affects the heat release.The pressure can promote the solder on the substrate surface wettability,and enhance the flowability of molten fillers,and oxide film were broken under high pressure. |
