Effect Of Continuous Rheological Extrusion On Microstructure And Properties Of Al-5Ti-1B Master Alloy

With the pursuit of light-weight in various fields,super strong and tough aluminum alloy materials have been favored by various industries.As we all know,aluminum alloy ingots with a fine and uniform equiaxed crystal structure can not only effectively reduce casting defects such as shrinkage shrinkage and thermal cracking,but also greatly improve the strength,toughness and reworkability of aluminum alloy ingots.Therefore,directly obtaining aluminum alloy ingots with a fine equiaxed crystal structure by controlling the casting process of aluminum alloys has become the primary choice for aluminum alloy manufacturers in the world to improve the performance of aluminum alloys.Among the many grain refinement methods,the refinement method of transforming the ingot from coarse equiaxed crystals to fine equiaxed crystals by adding Al-Ti-B refiner to aluminum and alloy liquid has become an aluminum production enterprise.best choice.Al-5Ti-1B alloy wire has been recognized by the world's aluminum producers as the best aluminum refiner.About75%of the world's aluminum processing companies are using this type of refiner.At present,Al-Ti-B master alloy manufacturers mainly use the fluoride salt method to prepare such master alloys.That is,the mixture of K₂TiF₆ and KBF₄ is added to the aluminum melt at about 800?,a certain intensity of mechanical stirring is applied,and the Al-Ti-B master alloy liquid is prepared by mixing the fluorine salt and the aluminum melt to produce an interface reaction,and finally continuous casting Continuously rolled into?9.5mm alloy wire.The preparation of intermediate alloy by the fluoride salt method is not only simple in preparation process,low in raw material price,but also easy to remove by-products of alloy reaction.However,a large amount of fluorine-containing gas will be released during the preparation process to cause environmental pollution,and long-term work will cause certain damage to the human body.Moreover,the by-products of the reaction can cause severe corrosion to the crucible and reduce the purity of the alloy liquid,thereby affecting the refinement performance of the alloy.This paper focuses on the preparation of Al-5Ti-1B intermediate alloy by continuous rheological extrusion technology to deter mine the optimal fusion and forming process of Al-5Ti-1B intermediate alloy wire,and discusses the use of the fluoride salt method.Titanium sponge replaced potassium fluorotitanate as the raw material for the preparation of the intermediate alloy melt.The substitution amount,alloying temperature,alloying time and pouring temperature of titanium sponge,the cooling water flow in the crystal wheel and the speed of the crystal wheel on the structure of the intermediate alloy and Refine the effect of the effect.The stability of the refinement effect of the master alloy was further verified by the refinement decay test.The main research is as follows:?1?The orthogonal flow process of Al-5Ti-1B master alloy was deter mined by orthogonal test:when the melt temperature was 850?,sponge titanium particles with a substitution rate of 25%were added to the aluminum melt for 10 minutes.,Adjust the melt temperature to 780?,and press the weighed fluorine salt pre-press block into the melt with a bell jar.After the fluorine salt block is completely dissolved,high-energy ultrasonic treatment is directly applied to the melt for 10 minutes,and then the alloy liquid melt is incubated for 20 minutes and then refined.The alloy liquid should be ultrasonic treated for 5 min before continuous rheological extrusion,so as to disperse the mesophase that may be deposited in the melt,and eliminate the component segregation in the alloy forming structure as much as possible.The parameters of the continuous rheological extrusion of the alloy liquid are:the flow of cooling water in the crystal wheel is 2.5L.h^-1,the pouring temperature is 740?,and the speed of the crystal wheel is 12.5 r.min^-1.The intermediate alloy wire prepared by this process refines the pure aluminum at 750?.After 20 minutes,the number of grains of the aluminum refinement sample is 130.61(pieces.mm^-2).?2?By studying the effect of titanium sponge substitution?0%,25%,35%?and alloying temperature on the chemical composition of the intermediate alloy:it is known that when sponge titanium is used to partially replace K₂TiF₆ to prepare intermediate alloys,the appropriate sponge The substitution amount of titanium can effectively increase the yield of master alloys with qualified component content.When the substitution amount of sponge titanium is 25%,the content of elemental Ti in the alloy is 5.08wt%,and the content of element B is 1.08wt%.?3?Al₃Ti phase in the Al-5Ti-1B structure prepared with 25%sponge titanium instead of K₂TiF₆ are mostly distributed in fine particles uniformly in the alloy structure,and the number is large.Bulk Al₃Ti phase.And as the reaction temperature increases,the size of Al₃Ti phase gradually increases,and the maximum size does not exceed 60?m.Its morphology changes with the increase of the reaction temperature:regular granular?relatively long and small strip?block.When the reaction temperature rises to 850?,the Al₃Ti phase in the master alloy is agglomerated.?4?The rheological extrusion parameters mainly affect the refinement effect of the intermediate alloy by changing the distribution of the second phase in the alloy structure.When the pouring temperature of the alloy liquid is 720?and the flow rate of cooling water is 2.5 L.h^-1,broken Al₃Ti particles appear in the alloy structure,the size of the TiB₂ cluster is small and the single TiB₂ phase in the cluster is very loose,without stickiness.With the increase of the cooling water flow rate,the Al₃Ti particle fragmentation phenomenon disappears,and the second phase is relatively uniformly distributed in the intermediate alloy structure.?5?The Al-5Ti-1B alloy prepared by the optimal process refines pure aluminum.At 750?,an intermediate alloy with a titanium content of 0.01wt%is added to pure aluminum.After 5 minutes,the aluminum grains are significantly refined.The coarse grains from about 900?m without refinement are transformed into fine equiaxed grains of 80?m.And in the subsequent 2 h holding time,the refining effect of Al-5Ti-1B on pure aluminum has no obvious decline.