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The main aluminum alloy extrusion process defect analysis and quality control methods

  First, shrink the tail

In some products, the tail end of the extrusion, the low magnification inspection, in the middle section of the sub-layer has the shape of trumpet-shaped phenomenon, known as shrink tail. Often you can see a class or second-class shrink shrink tail end of two cases. Located in the center of a class of contraction tail portion of the article, it was wrinkled like cracks or funnel-shaped holes. II products shrink tail located 1/2 radius area, a ring or crescent-shaped cracks. Sometimes appears continuous or discontinuous layer of substandard products from cracks or signs of cracks at the surface layer 0.5-2mm, someone called it the end of the third class shrinking.

Forward extruded products generally shrink tail longer than the reverse squeeze, soft alloy longer than the hard alloy. Forward extruded products showed more contraction tail ring substandard layer, back extrusion products shrink more performance for the center tail funnel-shaped.

Metal extrusion-to-back, piled in corners or on the extruder barrel shims ingot epidermis and foreign inclusions flow into article form a secondary condensing tail; when the remnant stay too short, insufficient feeding center of the product, then the formation of a class of contraction tail. From the end of the forward end shrink gradually become lighter or even disappear completely.

The main causes of reduced tail 1, the remnant left cut too short or article does not comply with the provisions of the tail length; 2, extrusion pad dirty, there is oil; 3, extrusion late squeeze too fast or sudden increases; 4, use a deformed extrusion pad (intermediate raised pad); 5, the extruder barrel temperature is too high; 6, extrusion cylinder and the extrusion axis misalignment; 7, ingot surface dirty, there is oil, not the car to segregation defects such as tumors and folding; 8, the extruder barrel sleeve is not smooth or deformed, not timely cleaning pad to clean lining. Prevention method 1, according to the provisions remain scrap and cut the tail; 2, to maintain clean mold; 3, to improve the surface quality of the ingot; 4, the reasonable control of the extrusion temperature and speed, steady squeeze; 5, except in special circumstances, is prohibited in work, greased mold surface; 6, appropriate cooling pads.

Second, the coarse crystal ring Some aluminum extrusion products after solution treatment at low magnification test piece is formed along the periphery of the article coarse recrystallized grains area, called coarse grain ring. Due to the different shape products and processing methods, can form a ring, arc and other forms of coarse grain ring. Depth coarse grain ring gradually decreases toward the front end with the rear end even completely

disappear. Subgrain formation mechanism of the region consists of hot extruded surface to form the article, the formation of coarse recrystallized grains district heating solution treatment. Coarse-crystalline main causes 1, extrusion uneven ' 2, the heat treatment temperature, holding time is too long, so that grain growth; 3, then the chemical composition of gold is unreasonable; 4, generally can be heat strengthened by heat treatment after the alloy has a coarse-crystalline produce, especially type 6a02,2a50 and other alloys, bar the most serious, can not be eliminated, can only be controlled within a certain range; 5, extrusion deformation or deformation is not sufficient, or in the critical deformation range, easy to produce coarse grain ring. Prevention method 1, extrusion cylinder wall smooth, to form a complete aluminum cover, reduce friction during extrusion; 2, deformation as fully as possible and even rational control of temperature, speed and other parameters; 3, to avoid the solution treatment temperature is too high or the holding time is too long; 4, with a porous die extrusion; 5, with anti-extrusion method and static extrusion extrusion; 6, with solid solution - drawing - aging production; 7, adjusted total gold content, increasing the recrystallization inhibiting elements; 8, the use of higher extrusion temperatures; 9, some uneven treatment alloy ingot, coarse grain during extrusion ring lighter.

Three, layering This is when the metal flow more uniform surface of the ingot mold and flows into the products along the front elastic region and the formation of an epidermal interface layered defects. Low times in the transverse test piece, the performance of the sub-layer cross-sectional edge portion has a defect. The main causes of layering 1, the ingot surface dirt or ingot greater segregation aggregates without wagon, tumors and other easy to produce a metal layer; 2, burrs or rough surface sticky oil, sawdust and other dirt, not cleaned prior to extrusion; 3, the die hole position is unreasonable, near the edge of the extrusion cylinder; 4, extrusion tool wear serious or extrusion cylinder to inner liner dirt, cleaning is not clean, and not be replaced; 5, pressing the pad diameter is too large; 6, Extrusion temperature higher than ingot temperature too much. Prevention method

1, the rational design of mold, timely inspection and replacement of defective tools; 2, unqualified ingot furnace is not installed; 3, after cutting residual material, should be clean, not stick lubricants; 4, maintaining the extrusion cylinder liner intact, or lined with pads cleared up. Fourth, bad welding Shunt die extrusion of hollow articles in the weld seam layered performance or not fully welding phenomenon, known as bad welding. Welding the main causes of poor 1, squeezing coefficient, low temperature extrusion, extrusion speed; 2, extrusion tool wool or unclean; 3, die oiled; 4, mold design inappropriate, inadequate or unbalanced hydrostatic pressure, the shunt hole design is unreasonable; 5, the ingot surface with oil. Prevention method 1, due to increase extrusion coefficient, extrusion temperature, extrusion speed; 2, rational design, manufacture molds; 3, Extrusion, extrusion gasket is not coated with oil, keep it clean; 4, the use of surface cleaning ingot. V. squeeze crack This is the extruded product lateral edges of the specimen showed a small arc cracking, cracking periodically along its longitudinal angled light when hidden under the skin, severe cracking of the outer surface to form a jagged, would seriously damage the metal continuity. Squeeze cracks caused by the extrusion process the metal surface by the mold wall is too large cyclic tensile stress is torn to form. Squeeze cracks main causes 1, the extrusion speed is too fast; 2, the extrusion temperature is too high; 3, extrusion rate fluctuations; 4, wool extrusion temperature is too high; 5, when the porous die extrusion die arrangement is too close to the center, so that the central metal inadequate supply, so that the flow rate difference between the center and the edges too; 6, ingot homogenization bad.

Prevention method 1, strict implementation of the heating and pressing norms; 2, often touring instrumentation and equipment to ensure the normal operation; 3, modify the mold design, meticulous processing, especially die-bridge, welding chamber and angular radius, etc. The design must be reasonable; 4, in the high-magnesium alloy to minimize the sodium content; 5, ingot homogenizing annealing to improve its plasticity and uniformity. Sixth, bubble Local skin metal and the base metal in a continuous or discontinuous separation, the performance of a single circular cavity or projections strip defects known as bubbles. The main causes of the bubble 1, extrusion extrusion cylinder and pressure pads with moisture, oil, dirt; 2, due to the squeeze tube wear, wear parts and the air between the ingot into the metal surface during extrusion; 3, the lubricant in the water; 4. Ingots itself loose, porosity defects; 5, the heat treatment temperature is too high, the holding time is too long, the furnace atmosphere humidity; 6, product hydrogen content is too high; 7, extrusion ingot barrel temperature and high temperature. Prevention method 1, tools, ingot surface remains clean, smooth and dry; 2, rational design extrusion cylinder and the extrusion with the size of the pad, always check the tool size, the extrusion cylinder Tatu appeared to be repaired, pressure pads can not exceed the difference; 3, to ensure clean and dry lubricants; 4, strict compliance with operating procedures extrusion process, timely exhaust, cut right, not anointed with oil, the elimination of scrap, billet and tooling to keep clean, not contaminated. Seven, from the skin This is the phenomenon of aluminum alloy extrusion products skin between the metal and the base metal to produce locally from falling.

The main causes of peeling 1, for alloy extrusion, extrusion cylinder wall sticky bush original metal forming, cleaning is not clean; 2, extrusion cylinder and pressure pads with inappropriate in the extrusion cylinder wall is lined with local residual metal; 3, lubricating Extrusion extrusion; 4, sticky metal or die on the job with a long die hole. Prevention method 1, column-for-alloy extrusion time to thoroughly clean up the extruder barrel; 2, rational design extrusion cylinder and squeeze the gasket mating dimensions, always check the tool size, squeeze the pad can not exceed the difference; 3, clean the residual metal on the mold. Eight, scratches Due to sharp objects in contact with the surface of the article, in the relative sliding mechanical injuries were caused by a single strip distribution, called scratch. The main causes of scratched 1, the tool assembly is not correct, the guide path, the table is not smooth, sharp edges or foreign body; 2, mold work to bring sticky work with metal shavings or mold damage; 3, internal lubricants sand or crushed metal shavings; 4, improper handling during transport operations, spreader inappropriate. Prevention method 1, timely inspection and mold polishing work with; 2. Check the product outflow channel, should be smooth, be properly lubricated guide path; 3, to prevent removal of the mechanical collision and scratches. Nine, bump hurt Products occasionally collide with other objects occur article in scar formed on its surface, called bump hurt. Bump the major causes of injury 1, table, rack and other structure is irrational; 2, baskets, rack and other metal inadequate protection; 3, no note gently operation. Prevention method 1, careful operation, gently; 2, polished off the sharp corners, with skids and soft material coated baskets, rack. Ten, abrasions Scars bunched distribution relative sliding or dislocation in the article surface caused by the surface of the extruded product with other objects or surfaces after contact with edge, called abrasions. The main causes abrasions 1, die badly worn; 2, due to high temperature ingot, aluminum die or die orifice hole stick work with damaged; 3, the extruder barrel fall into graphite and oil dirt; 4, the article ran each other, so that the surface scratches, extrusion flow with uneven, causing the products do not follow a linear flow, resulting in material and material with the guide path, bench abrasions. Prevention method 1, timely check and replace defective mold; 2, the heating temperature control wool; 3, to ensure extrusion cylinder and wool surface clean and dry; 4, control the extrusion speed, to ensure uniform speed. XI, mold marks This is a longitudinal uneven surface of the extruded article traces all extruded products have varying degrees of mold marks. The main causes of mold marks The main reason: mold work can not be achieved with absolute smoothness. Prevention method 1, to ensure mold work with smooth surface, smooth, no sharp edges; 2, reasonable nitriding treatment to ensure high surface hardness; 3, properly repair mode; 4, reasonable design work with, work with not too long. Twelve, twisting, bending, wave Longitudinal cross-section of the extruded product angular deflection phenomenon occurs, called twist. Products longitudinally curved or straight blade without bending phenomenon known. Continuous undulating phenomenon occurring products called longitudinal waves. Twisting, bending, the main causes waves 1, the die orifice design arrangement is not good, or working with a size distribution is unreasonable; 2, the die hole machining accuracy is poor; 3, not the right way to install guide; 4, improper repair mode; 5, extrusion temperature and velocity inappropriate; 6, the article is not pre-treatment solution pre-straightening; 7, cooling uneven line heat treatment.

Prevention method 1, engage in high mold design, manufacturing level; 2, install the appropriate guide path, traction extrusion; 3, with partial lubrication, maintenance mode plus diversion or alter the vent hole design to adjust the metal flow rate; 4, rationally adjust the extrusion temperature and speed, so that a more uniform deformation; 5, due to lower or raise the solution treatment temperature of solution treatment temperature; 6, line quenching ensure uniform cooling. XIII, hard bend Extruded products suddenly bent somewhere in the longitudinal direction, known as a hard bend. The main causes of hard bend 1, extrusion speed unevenness sudden change from low-speed, low speed or the high speed suddenly changed, and suddenly stop, etc; 2, during the extrusion process rigid moving products; 3, extruder uneven work surface. Prevention method 1. Do not stop or suddenly change the extrusion speed; 2, do not hand suddenly move profiles; 3, to ensure a smooth feed station and the discharge roller smooth, no foreign body, laminate unimpeded. Fourth, Pock This is extruded products surface defects, surface of the article refers to a continuous sheet of fine uneven punctate abrasions, pitting, beans, and other metals. Pock main causes 1, mold hardness enough or hard and soft uneven; 2, the extrusion temperature is too high; 3, the extrusion speed is too fast; 4, mold work with a long, rough or sticky metal; 5, pressing wool too long. Prevention method 1, to improve working with mold hardness and hardness uniformity; 2, according to procedures heated extrusion cylinder and ingot, extrusion speed appropriate; 3, the rational design of mold, reduce operating with surface roughness to enhance surface inspection, repair and polish; 4, using reasonable ingot length. Fifth, the metal is pressed into Extrusion process will be pressed into the surface of the article metal debris, called metal pushed. Metal pressed into the main causes: 1, wool tip faulty; 2, the inner surface sticky wool metal or lubricating oil containing metal debris and other dirt; 3, extrusion cylinder is not clean, there are other metal debris; 4, Ge ingot into other metallic foreign body; 5, there is slag wool.

Prevention method 1, remove burrs on wool; 2, to ensure wool surface and an internal lubricant clean and dry; 3, clean out the mold and extrusion barrel metal debris; 4, high-quality wool. Sixteen, nonmetallic pushed Within extruded products, pressed into the outer surface of the black stone and other foreign matter, known as non-metallic pushed. After the foreign body within the article presents scraped surface depressions of varying sizes, it would undermine the continuity of the product surface. Non-metallic pressed into the main causes 1, graphite coarse granularity or agglomerate, containing uneven mixing water or oil; 2, the flash point of the low cylinder oil; 3, cylinder oil and graphite ratio inappropriate, excessive graphite. Prevention method 1, the use of qualified graphite, keep dry; 2, filtration and the use of qualified oil; 3, control the ratio of good lubricating oil and graphite. XVII surface corrosion It has not been surface-treated extruded products, after its surface with the outside medium chemical or electrochemical reaction, causing local damage arising from surface defects, known as surface corrosion. Corrosion product surface loses metallic luster, severe corrosion products produce gray surface.

The main causes of surface corrosion 1, products in contact with water, acid, alkali, salt and other corrosive media in the production, storage and transportation process, or in a humid atmosphere and long-term parking; 2, alloy composition ratio improper; Prevention method 1, to keep the product surface and production, storage clean environment, dry; 2, control the content of the alloy elements. Eighth, orange peel Extruded products, like orange peel uneven surface appear like folds, also known as surface folds, which is caused by the extrusion of coarse grains, the more coarse grains, wrinkles more obvious. The main causes of cellulite 1. Ingots uneven, the equalization process is not sufficient; 2, extrusion conditions unreasonable, Jie into a coarse grain products; 3, excessive tension leveling. Prevention method 1, the reasonable control of homogenization treatment process; 2, deformation as evenly as possible (controlled extrusion temperature, speed, etc.) 3, control the amount of straightening is not too large. Ninth, uneven Regional products, changes in the thickness of the plane after extrusion appear sunken or raised, usually do not come out with the naked eye, by surface treatment or bone shadow shadow detail appears.

The main causes of uneven 1, working with poorly designed mold, mold repair is not in place; 2, the vent hole or front room the right size, the intersection area profiles pull or swelling of force resulting in small changes plane; 3, uneven cooling process, the thick portion or intersection portion slow cooling, resulting in varying degrees of the plane shrinkage during cooling; 4, due to the thickness of the disparity, the thick part of the transition area or other parts of the organization and differences in the organization increases. Prevention method 1, improve the mold design, manufacturing and repair mode level; 2, to ensure uniform cooling rate. XX chatter This is the period of the lateral surface of the extruded article stripe defects. Wherein the surface of the article was laterally continuous periodic stripes, stripe curve shape and mold the work coincides with a severe bump obviously feel.

The main causes of chatter 1, extrusion axis causes due to equipment jitter forward, causing the metal outflow hole shake; 2, due to the outflow of metal mold caused die hole shake; 3, mold support pad inappropriate, poor mold stiffness, jitter in extrusion pressure fluctuations. Prevention method 1, the use of qualified mold; 2, the mold to be used to install a suitable support pad; 3, adjust the equipment. Twenty-one inclusions

The main causes of inclusions Because mixed with metallic or non-metallic inclusions blanks on procedure undetected, remaining in the article after extrusion surface or inside. Prevention method Strengthen the inspection of blanks (including ultrasound), to put an end to contain metallic or non-metallic inclusions in the slab into the extrusion process. XXII, water marks Shallow white surface of an article or black irregular light waterline marks, called water marks.

The main causes of water marks 1, after washing and drying is not good, the product surface residual moisture; 2, rain and other causes of product surface residual moisture, not timely handle clean; 3, aging furnace fuel moisture, water cooling products after aging condensation on the surface of the article; 4, aging furnace fuel is not clean, sulfur dioxide corrosion or dust contaminated surface combustion products; 5, the quenching medium is contaminated. Prevention method 1, to maintain product surface is dry and clean; 2, control the moisture content and cleanliness aging furnace natural materials; 3, strengthen the management of quenching medium. Twenty-three gap Ruler laterally superimposed on the extruded product of a plane, between the ruler and the face showing some of the gap, called the gap. The main causes of the gap Metal flow straightening uneven or improper finishing operation squeezed. Prevention method Rational design, manufacture molds, to strengthen the repair mode, in strict accordance with regulations controlling the extrusion temperature and extrusion speed. XXIV uneven thickness Extruded products the same size in the same cross-sectional or longitudinal wall thickness thin thick, uneven phenomenon, called uneven thickness.

The main causes of uneven thickness 1, mold design unreasonable or improper mold assembly; 2, extrusion and extrusion needle cylinder not in the same center line, the formation of an eccentric; 3, extrusion cylinder liner wear is too large, the mold can not be firmly fixed, and the formation of an eccentric; 4, ingot rough uneven wall thickness itself, after primary and secondary extrusion, still can not be eliminated, after squeezing wool uneven wall thickness, by rolling, not trimmed after stretching; 5, lubricants applied unevenly, the metal flow unevenly. Prevention method 1, optimize mold design and manufacturing, assembly and adjustment is reasonable; 2, adjust the extruders and extrusion tooling center; 3, the selection of qualified stock; 4, the reasonable control of the extrusion temperature, extrusion rate and other parameters. XXV, expanding (and export) Both sides of the trough, and so-shaped extrusion products out oblique defects, called flaring, defects to the ramp, called a parallel port. Expansion (and) the main causes of mouth 1, grooved or two similar trough-shaped profiles or profiles of "leg" (or a "leg") of the metal flow rate uneven; 2, working with both sides of the groove bottom uneven flow rate; 3, improper stretching straightening machine; 4, the products out of the die hole, the online solution treatment uneven cooling.

Prevention method 1, and strictly control the extrusion speed and extrusion temperature; 2, to ensure uniformity of cooling; 3, the correct design and manufacture of molds; 4, and control of the extrusion temperature and speed, correct installation tooling. XXVI, straightening marks Spiral stripes generated when the squeeze roller straightening products, called straightening marks, all on roller straightening products can not avoid straightening marks. The main causes of straightening marks 1, straightening roller surface of a prism; 2, through the large curved products; 3, too much pressure; 4, roller straightening roll angle is too large 5, products ellipse degree. Prevention method Take appropriate approach be adjusted according to the causes. Xxvii, stop marks, instant prints, bite marks Stops when pressing squeeze generated surface of the article and perpendicular to the extrusion direction of the strip stripes, known as stop mark; during the extrusion process to produce the product surface and perpendicular to the extrusion direction south linear or striped ribbon , known as bite marks or instant prints (commonly known as "false stop marks") When squeezed, work stably adhered to the attachment surface of the belt, and instantly fall in extruded article adhesion surface pattern. Stop squeezing when working with stripes, known as stop mark; stripes appear in the extrusion process, called an instant impression or bite marks, will sound when squeezed. Stop marks, instant prints,

the main causes of bite marks 1, ingot heating temperature variations or mutations extrusion speed and pressure; 2, the main pieces of the mold design, manufacturing defective or assembly uneven, there is a gap; 3, perpendicular to the extrusion direction of the external force; 4, the extruder is not running smoothly, there is creeping phenomenon.

Prevention method 1, high-temperature, slow, uniform compression, extrusion pressure is kept stable; 2, to prevent vertical extrusion direction of external force to the product; 3, the rational design of the mold, the correct choice of mold material, size fit, strength and hardness. Twenty-eight, the inner surface scratches Scratch the inner surface of extruded articles produced in the extrusion process, known as the inner surface scratch.

The inner surface of the main causes abrasions 1, extrusion needle stick metal; 2, low temperature extrusion needle; 3, extrusion pin surface quality is poor, there is bump injury; 4, extrusion temperature, speed control is not good; 5. Improper ratio of extrusion lubricants; 6, greased uneven. Prevention method 1, to improve extrusion cylinder and the extrusion temperature needle, control the extrusion temperature and extrusion speed; 2, to enhance the lubricating oil filter, always check or replace oil, grease should be uniform, moderate; 3, to keep the surface clean wool; 4, the timely replacement of defective molds and extrusion needle, and kept pressing mold surface clean, bright and clean. Twenty-nine, the mechanical properties of substandard Extruded products, hb, hv other mechanical properties indicators do not meet the technical requirements of the standard or very uneven, called the mechanical properties of discord. Mechanical properties of the main causes of failure 1, the chemical composition of the main elements in the alloy excessive or unreasonable ratio; 2, extrusion or heat treatment process is unreasonable; 3, ingot or billet poor quality; 4, line quenching temperature did not reach enough of quenching or cooling rate; 5, improper artificial aging process.

Prevention and control measures 1, in strict accordance with the standard control of chemical composition or the development of effective internal standard; 2, using high quality ingot or billet; 3, optimization of extrusion process; 4, strict implementation of quenching system; 5, the strict implementation of the system and control the artificial aging furnace; 6, strict temperature and temperature control.

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