1 Aluminum ingots and extrusion cracks
After the aluminum ingot solidifies in the crystallization process, the multiple stress formed by the aluminum ingot exceeds the tensile strength of the aluminum ingot itself and causes cracking of the ingot, resulting in crack propagation during the extrusion to become a waste product.
There are two kinds of cracks in aluminum ingots: First, the cracks generally crack along the crystal, and the cracks are blackened. The cracks are oxidized and the cracks are jagged and irregular in shape. The first is that the cold cracks are cracked from the crystals, and the cracks are not oxidized. Polygons shine.
Preventive measures: scientific and reasonable control of aluminum alloy chemical composition and impurity content; to avoid overheating of molten aluminum and stay in the furnace too long; reasonable formulation of casting process, accurate control of casting temperature and casting speed; aluminum liquid supply and cooling should be uniform Prevent and avoid the inclusion of foreign inclusions cast liquid aluminum and other measures to effectively avoid cracks in aluminum ingots to create high-quality aluminum alloy extrusion products to create the preconditions.
The squeezing cracks often produce saw-tooth cracking near the edges of sharp corners, sharp corners, or thicker steps of aluminum products. Due to impure aluminum alloy, excessive impurities, poor thermoplasticity; high billet heating temperature, grain coarsening, so that the metal breaking resistance decreased; temperature control instrument failure, high extrusion temperature, extrusion speed out of control, suddenly speed up, increase Large deformation stress of the extruded thermoplastic, the metal near the outer layer of the die wall is torn into zigzag or sub-crack due to excessive tensile stress; the deformation of the extruded thermoplastic is uneven; the surface metal is subject to greater friction and additional tensile stress : When the transient stress exceeds the tensile strength of the metal, squeezing cracks are generated. Under the action of the external force, the crack propagates from the surface inward to the fracture.
Preventive measures: Strengthen the inspection of aluminum alloy materials, impurity content exceeds the standard and the original organization is not qualified not put into production; strict verification of temperature control instruments in production, temperature control accuracy must reach ± ​​1.5 °C; for different grades of aluminum alloy billet, develop corresponding The reasonable heating temperature ensures uniform heating; the extrusion speed and the amount of extrusion deformation for different brands of aluminum alloys are formulated so that the thermoplastic deformation is as uniform as possible; the design of the mold structure is improved; the angular positions of the extrusion section are as large as possible; It shows that pre-uniform annealing of aluminum ingots (540°C-560°C, fast cooling for 4-6 hours) can reduce the extrusion force by 15%-25%, increase the extrusion speed by 10%--15%, and significantly increase the thermoplasticity, etc. The above measures can effectively prevent and avoid the occurrence of crush cracks.
2 air bubble
Due to the gas inside the aluminum ingot and the air that is being blown during the extrusion process, the air expands during the extrusion and subsequent heat treatment, causing the surface to bulge out of the air bubble formed by the air bubble, losing the appearance of the goods and affecting the quality. Due to the looseness, shrinkage, pores, blisters, internal cracks, and coarse crystals of aluminum ingot billets; unclean tubing, oil, dirt, erosion, and abrupt changes in drum shape; preheating temperature of the extrusion cylinder is too high; extrusion The wear of the cylinder and the press pad is severe and the press fit is improper; the extrusion speed is out of control, the aluminum metal is filled too fast, the exhaust gas is not smooth, the aluminum metal adheres to the aluminum product and other factors, and all cause the aluminum product to foam and wrinkle.
Precaution. Improve the quality of aluminum ingots, select high-quality aluminum ingots and strict aluminum humans and pre-inspection inspections; replace severely worn extrusion barrels and extrusion pads in time and keep them clean and smooth; control the heat treatment atmosphere to prevent water vapor from entering the human body. For the lubrication of extruded gaskets and molds, adjust the extruder to make the movements evenly coordinated, formulate a reasonable extrusion speed and extrusion deformation amount to ensure the exhaust flow; the preheat temperature of the extrusion cylinder should be lower than the aluminum billet heating temperature 25 °C - 35 °C; to prevent excessive lubricant, timely removal of aluminum oxide shell and corrosion of dirt and other measures, can effectively prevent aluminum products from foaming and skinning, to achieve quality indicators.
3 bruises
The slight scratching of aluminum products not only makes the surface unsightly, but also drastically reduces mechanical mechanical properties and durability. Severe scratches on aluminum products cannot be used and become waste products, causing economic losses.
Due to the large surface roughness of the extrusion model, there are deeper cold processing tool marks, wear marks and bump marks, which can scratch the surface of aluminum products and produce bump marks; the mold is hard and wear-resistant, and the die surface is approximately 450°C- The aluminum metal billet at 500°C is in contact with the mold for a long time. Excessive tempering causes the hardness of the mold to decrease and soften. Due to the fierce metal plastic flow during the extrusion of the aluminum product and the strong friction between the mold cavity, the groove of the mold surface will be deepened, the surface of the aluminum product will be rougher, and the commodity surface will be lost; the assembly of the extrusion tool and die will be unreasonable and the clearance will be too large, resulting in heat Plastic aluminum metal from the mold hole in the process of contact with the mold and equipment and poor, resulting in serious scratches; pressure-type catheter and guideway improper assembly, or extrusion cylinder with aluminum metal oxide hard shell, slag, dust Foreign matter such as sand enters the die hole and scratches the work belt of the die, causing aluminum products to scratch.
Precaution. The surface of the extrusion die is strongly hardened to improve the red hardness, abrasion resistance and scratch resistance. The high quality refined die steel has high purity, less impurities, fine grains, small carbides, etc. Features such as excellent performance, chemical composition, and even organization, or the use of steel-bonded cemented carbide for the manufacture of molds, heat treatment by ramming and compound hardening, making the mold work surface high hardness, red hardness, wear resistance, fatigue resistance, and resistance Occlusion, anti-adhesive, anti-corrosion and anti-scratch properties, while the steel substrate has a high toughness, hard inside just gives a high life; choose a better working band width, after the production of a certain aluminum products, polished mold surface and work Belts; ensure assembly accuracy of tooling and extrusion equipment; often lubricate guides and conduits. The use of the above measures can effectively prevent aluminum product surface scratches and ensure that the aluminum product has excellent internal quality and surface quality.
4 Overheated
Due to overheating of aluminum ingots or incoordination of aluminum ingots with more flammable materials and failure of temperature control instruments, the heating temperature is too high, crystal grains grow significantly, local melting and oxidation of grain boundaries occurs, grain boundary bonding force decreases sharply, and brittleness increases. , The toughness is drastically reduced and the mechanical and mechanical properties are poor, resulting in the scrapping of aluminum products.
Precaution. Selection of high-precision WJ-1 microcomputer temperature control, can make the temperature control accuracy of ± 1.5 °C; strengthen heating equipment maintenance and inspection to ensure that the temperature within the furnace chamber uniform; strict inspection of aluminum ingot billet, no oil, etc. Combustibles, keeping the billet clean; formulating advanced and reasonable thermal processing procedures, careful operation and other measures to effectively avoid overheating and overheating, thus ensuring that the aluminum products are qualified for their organizational performance and surface quality.
5 Plastic deformation
Aluminum products with poor light plastic deformation become defective products, and those that become heavy waste products. Poor mold design, too long cantilever, leading to plastic extrusion of aluminum alloy during hot extrusion before and after the flow along the surface of the working belt surface, resulting in uneven plastic deformation, causing aluminum products to form a wavy asymmetric distortion; aluminum product design structure is too Complexity and great wall thickness difference result in insufficient rigidity of the weak parts, local stress concentration, and uneven aluminum metal flow rate. If the aluminum metal is suddenly blocked in the process of thermoplastic deformation, hard bending of the aluminum product will occur, resulting in blockage, sloppy cars, and the formation of twisting waves, resulting in poor plastic deformation.
Precaution. Scientifically and reasonably design molds to avoid overhanging, overlong and installation extrusion guides; strictly control the extrusion temperature and extrusion speed, ensure uniform plastic deformation, avoid midway stop; reasonably and accurately calculate the length of the blank to avoid Material; heating the first part of the product inspection, found problems and timely maintenance of equipment to ensure the normal operation of the equipment; adjust the extrusion temperature, extrusion speed and process parameters. By making them coordinate with each other and other measures, it can effectively prevent the plastic deformation of aluminum products from being poor and achieve high quality and high output.
6 Bad welding
The poor welding of aluminum products results in inferior mechanical mechanical properties of the welds, which makes the aluminum products vulnerable to cracking at the welds under external forces, causing them to become waste products and cause losses. Oxide, oil dirt and extrusion residue on the surface of the aluminum ingot billet separates the weld seam, lowers the extrusion temperature, and causes poor thermoplasticity; the extrusion force and extrusion time are insufficient; the welding cavity is too small and the cavity is too small Insufficient pressure and so on.
Precaution. Adopt advanced extrusion equipment, advanced technology and advanced technology, and strengthen scientific management; correctly and rationally design molds to ensure that aluminum metal plastic flow uniformity and welding; use of high-quality aluminum ingots to ensure that the surface is smooth and no foreign body, before extrusion Clean the surface of clean aluminum billets; formulate reasonable extrusion temperature and extrusion speed for different brands of aluminum alloys; ensure that extrusion equipment and working parts of the tools and molds are free from foreign materials, etc., and obtain high-quality smooth welds to make them high Mechanical mechanical properties and commercial surfaces are not easily cracked by external forces.
7 Ripple and Size Fluctuation
Due to the instability of the extruder, serious jitter, uneven flow of aluminum metal through the die cavity, large thickness and uneven cooling of aluminum products, and uneven cooling, resulting in the formation of ripples on the surface of the aluminum products; improper positioning of the die and the barrel wall, or misalignment of the die Oblique, so that the extrusion stress and extrusion speed change, causing uneven thickness of aluminum products and extrusion length, resulting in thickness and size fluctuations, seriously affecting the quality and durability of aluminum products.
Precaution. Maintain the extrusion machine to achieve the required precision, work smoothly without jitter; Correct and ensure that the mold work belt to obtain a uniform metal plastic flow; Control cooling rate, to ensure uniform cooling of aluminum products; Selection of a high-quality aluminum ingot; Design precision Durable extrusion die and the development of a reasonable amount of extrusion and extrusion speed; to ensure that the extruder hydraulic system without air traps and other measures, can effectively prevent and avoid aluminum products ripple and size fluctuations to ensure the quality of aluminum products.
8 Tissue lines, mould lines and burrs
This defect is related to the casting process, the extrusion process and the mold, which seriously affects the appearance and quality of aluminum products. Due to the inhomogeneity of the macroscopic or microscopic structure of the aluminum ingot and the inhomogeneous treatment of the aluminum ingot, the alloy composition of the aluminum ingot is different from the crystallization method. It is easy to form different grain sizes and different crystal directions, resulting in ribbon lines that are in line with the extrusion direction. When aluminum ingots are folded and slag inclusions, they are often unfavorably fed from the edge gaps to make aluminum metal. Strong thermoplastic flow; eccentricity of the extrusion force causes billet scale and other foreign materials to squeeze into the working belt and die holes; the gap between the aluminum billet and the barrel is too large, or slag inclusion, overheating, and sudden changes in the length of the working belt will occur. Causes tissue lines, mold lines, and burrs to occur.
Precaution. When the crystals of aluminum ingot are solidified, they are uniformly and rapidly cooled, and the aluminum ingots are subjected to grain refinement; high-quality aluminum ingots with high purity, little impurities, fine grains, and no slag inclusions are used; The larger gap between the press tube and the press pad is ≤ 1. Omm; ensure the accuracy and concentricity of the extrusion die, reduce the surface roughness of the die; strengthen the inspection of the first aluminum product, reach the first-class quality products before mass production; after producing a certain number of products, mold release polishing surface, and timely Clean up the aluminum oxide shell, dirt and foreign matter in the extrusion cylinder and the extrusion pad, etc. to effectively eliminate tissue lines, mold lines and burrs to ensure that a high-quality aluminum product is produced.
9 laminated
Aluminum laminate defects, not only the surface is not beautiful, making it mechanical and mechanical properties of the poor, under the external force of the laminate is easy to crack and become waste. Aluminum ingots have casting defects such as folding, delamination, and slag inclusions; the cylinder and the press pad are heavily worn, the die hole is too close to the inner wall of the cylinder, and the blank is fed from the improper edge gap; Erosion, bulging or sag, there are too many residual aluminum metal oxide shells, and lubricant is retained; the surface layer metal of the blank flows along the boundary of the elastic region at the front end of the extrusion die, resulting in the lamination defects of the aluminum product.
Precaution. Use high-quality aluminum ingots without slag inclusion, delamination or folding to increase the elasticity, plasticity and toughness of the billet and reduce the anisotropy; strict inspection of the aluminum ingot, which can not be used for those who have serious defects; clean and squeeze after the pre-class shift Foreign material in cylinder and extrusion pad: Correct concentricity of extrusion die and extrusion cylinder, replace defective die and extrusion parts in time, reduce the amount of grease and lubricant; design advanced advanced extrusion die and vacuum melting steel , Electroslag remelting steel manufacturing extrusion molds and other measures. Effectively eliminate aluminum laminates and ensure the quality and durability of aluminum products.
10 bright grain and lace-like tissue
The primary crystals of the poorly-dissolved solid solution with a low content of alloying elements in the aluminum ingot structure are brighter than the normal tissue, and the dendrites are coarse and the network is thin. Their hardness and mechanical properties are lower than normal structures. The formation of bright grains is due to the fact that the temperature of the hopper is low during the casting process. At the bottom of the crystallization process, low-content primary crystals form a solid solution and grow continuously, gradually forming bright grains.
Precaution. Funnel heat conductivity is better, the surface should be smooth, the funnel coating needs to be uniform; the funnel should be fully preheated, the funnel sinking liquid should not be too deep and scientific and reasonable casting temperature: casting liquid aluminum should be uniform and prevent the bottom of the funnel attached to the liquid aluminum And other measures to effectively eliminate the poor mechanical properties of shiny grains.
The line-shaped lace formed at the grain boundaries resembles feather-like casting twins. The microstructures are parallel to each other. The boundaries are wavy or sawtooth, which not only affects the appearance but also affects the performance. Due to the improper allocation of chemical composition of aluminum ingots; overheating of the melt and excessive lengthening during the stay; too small diameter of the filter tube, high casting temperature, too short a crystallizer, and failure of the modifier. Precaution. The chemical composition of aluminum ingots should be scientific and reasonable, and impurities are forbidden to exceed the standards. The appropriate filtration system and crystallization device should be selected. Precise control of casting temperature and time; appropriate and timely addition of quality modificators should effectively prevent lace formation and ensure the quality of aluminum products.
11 Contraction
Because of the nodule on the surface of the aluminum ingot, it is easy to cause eccentricity between the extrusion tube and the shaft; due to the high extrusion temperature at the later stage of extrusion, the extrusion speed increases, resulting in surface metal flow along the interface between the extrusion pad and the rear elastic zone. Inside the aluminum product, an annular shrinkage is formed; when the extrusion is reversed, the cavity pressure is insufficient. In addition to the insufficient metal replenishment, it is easy to produce a shrinkage of the center funnel and become a waste product. Precaution. Strengthen the quality inspection of aluminum ingots before they enter the warehouse and put into operation. Unqualified aluminum ingots are not put into production. If nodulated aluminum ingots are found, they can be put into production after removal of nodules. Firstly, extrusion equipment should be fully inspected and repaired prior to extrusion. The tool and die meet the standards to ensure the accuracy level and concentricity; use reasonable extrusion speed and extrusion temperature; timely replace super-excessive extrusion parts and tooling; use electroslag remelting high-quality die steel and surface strengthening heat treatment new manufacturing process Extrusion die; selection of high-quality aluminum ingots and advanced extrusion technology and other measures. Effectively eliminate aluminum defects caused by shrinking.
12 Scratches
Extruded aluminum products not only lose the appearance of aesthetic goods, but also dramatically reduce mechanical mechanical properties and affect durability. Light scratches become defective, and severe scratches become waste. Aluminum products are scratched due to infusible inclusions in aluminum ingots, molds, and process and operation factors.
Aluminum ingot inclusions: due to chemical reactions in the smelting process, the aluminum liquid reacts with oxygen and water in the air to generate A1203, MgO, Si01 and A1203: MgO inclusions; A1-Ti-B residual refiner and Ti-B The coarse particles of the master alloy, the hard-spots of the refractory bricks and the protective coating on the tools cause scratches on the aluminum products. When the mold is partially broken off due to die mouth and working belt during the extrusion process, the residue is hung in the working belt; the obstructing wall of the welding is removed when the mold is repaired, and the stress concentration is blocked when the mold or mold has sharp edges and edges; the mold section The distance from the extrusion tube is too small, the wall mold inclusions flow without the inclination and surface roughness of the mold, resulting in the residual aluminum accumulation and other factors that lead to aluminum product scratches caused by the mold. Process and operation: Extrusion speed is too fast, causing uneven flow velocity, making fine and hard inclusions easy to flow laterally and aluminum metal being blocked at non-smooth locations such as die ports and working belts. Hung scratches are formed.
Precaution. Improve the quality of aluminum ingots, use ceramic filter plates to filter out inclusions; improve mold repair quality and meet technical requirements; improve mold design and manufacturing quality; use soaked aluminum ingots, constant temperature deceleration, reduce extrusion force, make aluminum metal The flow rate is even and the force condition of the mold is improved; the surface of the aluminum ingot is cleaned before it is squeezed and the inclusions are prevented from entering the barrel, and the scratches are effectively eliminated.
In short, after comprehensive management, 12 aluminum alloy extrusion products can effectively eliminate the above-mentioned defects, achieve high quality, high production, long life, and beautiful appearance of the goods, create a brand, bring vitality and prosperity to enterprises, and have significant technical and economic benefits.
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