Study On Microstructure And Properties Of Over-fired Aluminum Alloy Welds

6xxx series aluminum alloy is mainly composed of Al-Mg-Si alloy elements.This series of aluminum alloys are heat-treatable reinforced aluminum alloys.This series of aluminum alloy has medium strength,good processability and good weldability.Therefore,this series of aluminum alloys are widely used in construction,vehicles,aerospace and other fields.These areas are closely related to people’s lives.In the event of a fire hazard,it may cause huge losses to people’s lives and property.Aluminum alloy usually appears in the form of structural parts,and the weld is the weak part in the structural parts.Therefore,it is of practical value to study the microstructure and properties of over-fired aluminum alloy welds and to study the changes in the microstructure and properties of over-fired aluminum alloy welds protected by fire protection measures.In this paper,6063-T6 aluminum alloy plates with a thickness of 3mm were used as experimental materials.The 6063-T6 aluminum alloy plates were welded by CMT welding method.4043 aluminum alloy welding wire was selected as the welding wire of this welding experiment.The welding process parameters are explored in order to obtain welds with good appearance,less welding defects and high strength.An intumescent refractory coating was selected.The aluminum alloy samples were coated with different thickness values and the coating curing time was at least 24 hours.Over-fired experiments were carried out on samples of aluminum alloy base metal,aluminum alloy welds(without fireproof coating protection),and aluminum alloy welds(with fireproof coating protection).The source temperature was calibrated using an S-type thermocouple.The temperature at the back of the aluminum alloy plate was measured using a K-type thermocouple.The thermal insulation effect of the fireproof coating is judged according to whether the sample is fused or not and the temperature on the back of the sample is different.According to the thickness changes of the fireproof coating before and after expansion,the expansion rate and expansionmultiple of the fireproof coating with different thicknesses can be calculated.The microstructures of the samples before and after the over-fired experiments were analyzed.Explore the growth pattern of the grains at the weld and the changes in the microstructure of the aluminum alloy at different backing temperatures.The aluminum alloy samples were subjected to tensile testing.Explore the changes in tensile strength,yield strength,and yield ratio of welds at different backing temperatures.The experimental results show that when the CMT pulse welding method is used to weld 6063-T6 aluminum alloy plate with a plate thickness of 3mm,when the wire feeding speed is 5.0m/min,the welding speed is 400mm/min,and the gas flow rate is22L/min,a better quality weld can be obtained.The microstructure of the weld is in the order of equiaxed crystals,columnar crystals and cell crystals from the center of the weld to the heat affected zone.When the aluminum alloy base material and weld are not protected by the fireproof coating,the over-burned tissue appears after the over-fired experiment.In the case of fireproof coating protection,no over-burned tissue appeared after the over-fired experiment.In terms of mechanical properties,samples without fireproof coating protection are directly fused when over-fired.The samples protected by fireproof coating did not produce obvious deformation,but their tensile strength and yield strength decreased slightly and plasticity increased slightly.