| T/R module, as signal sending and receiving module, is widely used in all kindsof phased array radar and its traditional packaging materials have many disadvantages,such as the large specific gravity and poor thermal conductivity. Aluminum matrixcomposites reinforced with high volume fraction SiC particles, which own threecharacteristics of low expansion, high heat conductivity and lightweight, is the idealreplacement material of this T/R electronic packaging module. However, due to theparticularity of module structure (built-in chip can’t overheat), the conventionalwelding method (such as melting welding) cannot form the true meaning of weldedjoint, so the insiders usually adopt the method of furnace brazing, but it is easy tocause overheating damage to the chip of the packaging module bottom. Technically,the poor weldability of the composites is hindering its application smoothly.Responding to the problems above, this paper puts forward a new method ofconnection: laser induce brazing. The laser, which can produce a controllableprecision heat source, is loaded in the upper surface and through the mechanism ofheat conduction the heat is conducted to the solder between the two plates through theupper plate in order to induce solder melts to form the good braze welding joint.Ensure that local heating zone is narrow and avoid the overheating phenomenon ofother parts.Through the establishment of the laser induce brazing heat source model and thededuced laser induce brazing moving point heat source heating quasi-steady stateequation of thin plate, the laser induce brazing temperature field numerical simulationand the following experimental verification have been done. The ideal temperaturefield as well as the process parameters (power334W, the welding speed is132mm/min, the coke+5mm, the laser spot diameter of0.2mm) is acquired. The resultsshowed that the simulated values of the thermal cycle curves agreed with themeasured values well.Based on the principle of solder and base metal matching, four kinds of solder is chosen in this paper, and the wetting spreadability test is respectively finished. Thetest results show that the wetting spreadability of the micro particles of Sn (wettingAngle≦3degree) and nanometer Al powder(wetting Angle is25degree) is betterthan AlZn25Si1(wetting Angle is48degree) and ZnAl7solder (wetting Angle is40degree), with the solder wetting of Sn spreadability being optimal.The test of laser induce brazing for the joint of the composite material showedthat the AlZn25Si1brazing seam is combined badly, its wettability is poor, the soldercan’t wet the bare SiC particles, with weak bonding force between parent metal; theZnAl7brazing seam is dense and well combined with the parent metal, presenting thestate of metallurgical combination; micro particles of Sn and parent metal interdiffuseand solder can better wet the bare SiC particles; the nanometer Al powder with strongatomic diffusion force can wet the bare SiC particles well, and the combinationbetween parent metal and brazing seam is good without flaws.Through the analysis of mechanical testing on joint after welds it is found thatthe average tensile-shear strength of AlZn25Si1joints is2.996N/mm2; the averagetensile-shear strength of ZnAl7joints is17.086N/mm2; the average tensile-shearstrength of micro particles of Sn joints is8.406N/mm2; the average tensile-shearstrength of nanometer Al powder joints is22.742N/mm2.Through the analysis of the fracture of joint after welds it is found that theAlZn25Si1fracture with the low tensile-shear strength occurred in the interfacebetween the brazing seam and the parent metal, which is characterized by the overallstripping, and that the other three kinds of joint fracture occurred in the brazing seamposition, thereby describing the physical nature and mechanism of laser inductionbrazing. |
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