The Effect Of Technological Factors On Cast-rolling Microstructural Of Hypoeutectic Al-Si Alloy

The hypoeutectic Al-Si alloy can be used as a Brazing solder due to its advantages such as low melting point,high ductility,and good melt filling properties.Brazing sheets made of Al-Si alloy are widely used in the production of automotive parts.At present,in the industry,hot-rolling method is commonly used to produce hypoeutectic aluminum-silicon alloy slab materials,which have high equipment investment and large energy consumption,resulting in high production costs.The continuous cast-rolling method has the advantages of short production flow,small energy consumption,and low equipment investment,can effectively reduce production costs.However,at present,the hypoeutectic Al-Si alloy slabs produced by the continuous cast-rolling method still have some difficulties.The slab material produced has the disadvantages of large Residual casting tissues,coarse grains and uneven distribution of chemical components.It is necessary to study and optimize the process parameters of continuous casting and rolling.In this paper,a series of studies have been conducted on the continuous cast-rolling production methods of hypoeutectic Al-Si alloys,by adjusting the continuous casting process parameters,and compared with the hot rolled slab microstructure.The microstructure of the cast-rolling slab was analyzed using an optical microscope,a scanning electron microscope and an energy spectrum analyzer;Measurement of melting temperature of aluminum-silicon alloy slabs by differential scanning calorimeter;Using mechanical properties and fracture morphology analysis to further verify the performance of the slab material.The test results show that:(1)The use of Sr as a modifier in the smelting process can effectively modify the eutectic silicon,To transform eutectic silicon from lath shape to fibrous shape or coral shape,and Sr modifier has a good metamorphic effect after 0.5h,the metamorphic effect is best after 4 hours,and the metamorphic effect is still not declining after 8 hours.In the industrial production process,the use of chlorine salt refining agent refining treatment has no significant effect on the effect of deterioration;(2)Compared with hot-rolled slabs,eutectic silicon refinement of the cast-rolling slabs is very noticeable,and the size is much smaller than hot-rolled slabs.However,the eutectic silicon distribution of the hot-rolling slabs is more uniform than that of the cast-rolling slabs,cast-rolling slabs will have a middle segregation of eutectic silicon;(3)The adjustment of cast-rolling process parameters has no obvious effect on the morphology of eutectic silicon.When the cast-rolling zone length is adjusted from 36 mm to 54 mm,the eutectic silicon middle segregation decreases first and then increases with the increase of the length of the casting zone.When the length of the casting zone is 48 mm,the size of eutectic silicon segregation is minimum.When the temperature of the front box is increased from 670°C to 675°C,there is no obvious change in the cast slab microstructure.When the temperature of the front box is increased to 680°C,the segregation size of eutectic silicon in the slab structure increases,and the center disperses outward.After the slab thickness increases from 6.5mm to 7.0mm,the segregation of eutectic silicon becomes larger and spreads outward from the center.When the slab thickness increases to 7.5mm,eutectic silicon accumulates on the surface of the slab,cause inverse segregation of eutectic silicon.The adjustment of the above process parameters has no significant effect on the morphology of eutectic silicon and has a greater impact on segregation.(4)After the heat treatment of the aluminum-silicon alloy slab,the morphology of the eutectic silicon changes from a coral shape to a spherical shape,and the eutectic silicon partially remelts,and the middle segregation of the eutectic silicon decreases.As the heat treatment temperature increases,the segregation of eutectic silicon decreases,increasing the toughness of the material.When using heat treatment at 540°C/3h,the eutectic silicon has the smallest segregation.The mechanical properties and fracture morphology were analyzed.As the heat treatment temperature increased,the tensile strength,yield strength and yield ratio of the cast slab decreased,and the elongation increased with increasing temperature.After the heat treatment,the dimple depth at the fracture surface was significantly deepened,and with the increase of the treatment temperature,the dimples were even smaller and denser.It is further illustrated that the heat treatment can effectively increase the toughness of the material,and the effect is best after being treated at 540°C/3h.(5)Aluminum-silicon alloy slabs are produced by continuous cast-rolling.The optimized production process is: Using Sr for 4h modification,the cast-rolling zone length is set to 48 mm,the front box temperature is set to 670°C,the slab thickness is set to 6.5mm,and aluminum-silicon alloy slabs are produced.heat treatment at 540°C/3h for the produced slabs.The aluminum-silicon alloy slab produced after the process optimization was subjected to the subsequent cold rolling process inspection,and successfully processed into a brazing plate with a thickness of 0.15 mm,and the plate was free from defects such as cracks and holes.