Aluminum alloy extrusion defect analysis and quality control method (1)

【China Aluminum Industry Network】 At the end of certain extruded products, after low magnification inspection, there is a trumpet-like phenomenon in the middle of the cross-section, which is called shrinking. You can often see one type of shrinking or two types of shrinking. One type of shrinkage is located in the center of the product, showing creased cracks or funnel-shaped holes. The type II shrinkage tail is located in the area of ​​the product radius 1/2, showing a ring or crescent-shaped crack. Sometimes there is a continuous or discontinuous layer of cracks or cracks on the surface 0.5-2mm away from the surface of the product. Some people call it the third type of shrinkage. The shrinking tail of a generally forward extrusion product is longer than that of a reverse extrusion, and the soft alloy is longer than the hard alloy. The shrinking of the forward extrusion product is mostly a ring-shaped non-integral layer, and the shrinkage of the backward extrusion product is mostly a center funnel shape. When the metal is extruded to the back end, the ingot skin and foreign inclusions accumulated on the dead ends or gaskets of the extrusion cylinder are discharged into the product to form secondary shrinkage. When the residue is too short, the center of the product is insufficient to be fed. Form a type of contraction. From the tail end, the tail shrinks gradually and disappears completely. The main causes of shrinking: 1. The residual material is too short or the tail length of the product does not meet the requirements; 2, squeeze pad is not clean, oily; 3. In the late extrusion period, the extrusion speed is too fast or suddenly increases; 4, the use of deformed extrusion pad (middle raised pad); 5, extrusion tube temperature is too high; 6, the extrusion cylinder and the extrusion axis are not in alignment; 7, the surface of the ingot is not clean, there is oil, no car segregation and folding and other defects; 8. The inner sleeve of the barrel is not clean or deformed, and the inner liner is not cleaned in time with the cleaning pad. Prevent method: 1, according to the provisions of the left material and cut tail; 2, keep the tooling clean; 3, improve the surface quality of the ingot; 4, reasonable control of extrusion temperature and speed, in the smooth extrusion; 5, except for special circumstances, it is strictly forbidden to grease the surface of the work or mold; 6, the gasket is properly cooled. Second, coarse-grained ring Some aluminum alloy extrusion products form a coarse recrystallized grain structure along the periphery of the product on the low-strength specimen after solution treatment, and are called coarse-grained rings. Because of the different shapes and processing methods of products, ring, arc and other forms of coarse-grained rings can be formed. The depth of the coarse-grained ring decreases gradually from the end to the front and disappears completely. The formation mechanism is the subgrain area formed by the hot extrusion on the surface layer of the product, and after heating and solution treatment, the coarse recrystallized grain area is formed. The main cause of coarse-grained rings: 1, extrusion deformation is not uniform; 2, the heat treatment temperature is too high, the holding time is too long, so that the grain grows; 3. The chemical composition of the gold is unreasonable; 4, the general heat-treatable alloy after heat treatment has a coarse-grained ring, especially 6A02, 2A50 and other alloy types, rods are more serious, can not be eliminated, can only be controlled within a certain range; 5, small deformation or deformation is not enough, or in the critical deformation range, easy to produce coarse grain ring. Prevent method: 1. The inner wall of the squeeze tube is smooth and clean, forming a complete aluminum sleeve, reducing the friction when extruding; 2. The deformation is as full and uniform as possible, and reasonable control of temperature, speed and other process parameters; 3, to avoid the solution treatment temperature is too high or the holding time is too long; 4, extrusion with porous die; 5, using the back extrusion method and the static extrusion method; 6, using solution treatment - drawing - aging method of production; 7, adjust the whole gold composition, increase the recrystallization inhibition element; 8, using a higher temperature extrusion; 9. Some alloy ingots are not treated uniformly, and the coarse crystal rings are shallow during extrusion. Third, layering This is a skin layering defect formed when the metal flow is relatively uniform and the surface of the ingot flows into the product along the interface between the die and the front end elastic zone. In the lateral low magnification test piece, there was a flaw in the edge of the cross section. The main causes of layering: 1. Dust on the surface of ingots or ingots with large segregation aggregates but not wagons, metal tufts, etc., tend to produce layers; 2. The surface of the blank has burrs or sticky oil, sawdust and other dirt. It has not been cleaned before extrusion. 3, the position of the die hole is irrational, close to the edge of the barrel; 4. The squeezing tool is worn out badly or the dirt inside the cylinder sleeve is squeezed. The cleaning is not clean and it is not replaced in time; 5, the difference between the diameter of the squeeze pad is too large; 6, extrusion cylinder temperature is too high than the temperature of the ingot. Prevent method: 1. Reasonably design molds, timely check and replace unqualified tools; 2. Unqualified ingots are not installed; 3, after cutting the residual material, it should be cleaned, not sticky lubricating oil; 4. Keep the lining of the extruding tube intact, or clean the inner lining with a gasket. Fourth, bad welding The phenomenon of delamination or incomplete welding of the welds in the hollow products extruded from the shunts at the welds is called bad welds. The main causes of poor soldering: 1, the extrusion coefficient is small, the extrusion temperature is low, the extrusion speed is fast; 2, squeezing wool or tools is not clean; 3, mold oiling; 4. Improper mold design, insufficient or unbalanced hydrostatic pressure, and unreasonable design of the shunt hole; 5, the surface of the ingot has oil stains. Prevent method: 1, increase the extrusion coefficient, extrusion temperature, extrusion speed; 2, rational design, manufacture molds; 3, squeeze tube, squeeze gasket is not oiled, keep clean; 4, the use of surface clean ingots. Fifth, squeezing crack This is a small arc-like cracking at the edge of the transverse test piece of the extruded product, which is periodically cracked at a certain angle along its longitudinal direction, hidden beneath the epidermis when light, and severely forms serrated cracks on the outer surface, which can severely disrupt metal continuity. Extrusion cracks are formed by the metal surface layer being torn by excessive cyclic tensile stress of the die wall during the extrusion process. The main cause of extrusion cracks: 1, the extrusion speed is too fast; 2, extrusion temperature is too high; 3, extrusion speed fluctuations; 4, extrusion wool temperature is too high; 5, porous die extrusion, the mold is too close to the center, so that the supply of the central metal is insufficient, so that the center and the edge of the flow rate difference is too large; 6. Ingot homogenization and annealing is not good. Prevent method: 1, strictly enforce the heating and extrusion specifications; 2. Regular inspection of instruments and equipment to ensure normal operation; 3, modify the mold design, meticulous processing, especially the design of the bridge, welding room and angular radius should be reasonable; 4. Minimize sodium content in high-magnesium aluminum alloys; 5. Ingots are homogenized and annealed to increase their plasticity and uniformity. Six, bubbles Local epidermis metal is separated from the matrix metal continuously or discontinuously, and it shows a defect of a circular single or strip-shaped cavity protrusion called a bubble. Bubble main causes: 1. The squeeze tube and the squeeze pad are filled with dirt, oil and other dirt when squeezed; 2. Due to the abrasion of the squeezing cylinder, the air between the worn portion and the ingot enters the metal surface during squeezing; 3, there is moisture in the lubricant; 4. The ingot structure itself has porosity and porosity defects; 5, heat treatment temperature is too high, holding time is too long, the atmosphere humidity in the furnace; 6, the product hydrogen content is too high; 7, extrusion barrel temperature and ingot temperature is too high. Prevent method: 1. The surface of the tool and ingot is kept clean, smooth and dry; 2, the rational design of the size of the extrusion tube and the extrusion gasket, often check the size of the tool, when the extrusion tube occurs when the belly must be repaired, the extrusion pad can not be poor; 3, to ensure that the lubricant is clean and dry; 4, strictly abide by the extrusion process operation, timely exhaust, cut properly, do not grease, completely remove the residual material, keep the billet and tooling clean and not be contaminated. Seven, from the skin This is a phenomenon in which aluminum alloy extruded products produce localized separation between the skin metal and the base metal. The main reason for skinning: 1. When alloy extrusion is performed, the liner formed by the original metal adheres to the inner wall of the extrusion cylinder, and the cleaning is not clean; 2. The extrusion cylinder and the press pad are not properly fitted, and the inner wall of the extrusion cylinder is lined with local residual metal; 3, the use of lubrication extrusion tube extrusion; 4, the mold hole with metal or mold work with too long. Prevent method: 1. Clean the squeeze tube thoroughly when changing the alloy extrusion; 2. Reasonably design the fit size of the extrusion cylinder and the extrusion gasket, often check the size of the tool, and the extrusion pad can not be out of tolerance; 3, timely clean up the residual metal on the mold. Eight, scratch Due to the sharp article and product surface contact, in the relative sliding caused by a single distribution of mechanical injuries, known as scratches. The main causes of scratching are: 1. The assembly of the tool is not correct, the guiding path and the worktable are not smooth, there are sharp corners or foreign objects, etc.; 2. Mold work tape has metal chips or mold work belt damaged; 3, lubricating oil with sand or broken metal shavings; 4. Inappropriate handling during transport and improper spreader. Prevent method: 1, timely inspection and polishing mold work belt; 2, check the product outflow channel should be smooth, can properly guide the road; 3. Prevent mechanical scratches and scratches in handling. Nine, bump injuries The scratches formed on the surface of products or products that collide with other objects are called bumps. The main causes of scratch damage: 1. The structure of worktables, shelves, etc. is irrational; 2. Material baskets, racks and other improper protection of metal; 3, did not pay attention to gently handle. Prevent method: 1, meticulous operation, take care; 2. Grind off the sharp corners and cover the material baskets and racks with wood and soft materials. Ten, bruises After the surface of the extruded product comes into contact with the edges or surfaces of other objects, a bundle of scars caused by relative sliding or misalignment on the surface of the product is called a scratch. The main cause of abrasions: 1, mold wear is serious; 2, due to ingot temperature is too high, die hole aluminum or die hole work belt damage; 3, into the cylinder squeezed graphite and oil and other dirt; 4. The products move against each other, causing scratches on the surface and uneven flow in the extrusion stream, causing the product to not flow in a straight line, resulting in scratches on the materials and materials, guide paths, and worktables. Prevent method: 1, timely check, replace the unqualified mold; 2, control the heating temperature of the wool; 3, to ensure that the surface of the extrusion cylinder and woolen material is clean and dry; 4, control the extrusion speed to ensure uniform speed. Eleven, mark This is a sign that the surface of the extruded product is uneven and uneven. All extruded products have different levels of mold marks. The main cause of mold marks: The main reason: the mold work belt can not be reached smooth. Prevent method: 1, to ensure that the mold work with a smooth surface, smooth, no sharp edges; 2, a reasonable nitriding treatment to ensure high surface hardness; 3, correct mold; 4, a reasonable design of the work zone, the work zone can not be too long. Twist, bend, wave The phenomenon of angular deflection of the cross section of the extruded product in the longitudinal direction is called twisting. The phenomenon that the article is curved in the longitudinal direction or the blade is not straight is called bending. The phenomenon of continuous undulations in the longitudinal direction of an article is called a wave. The main causes of twisting, bending, and waves are: 1, mold hole layout is not good, or the work belt size distribution is not reasonable; 2, poor precision machining die hole; 3, no suitable guides are installed; 4, improper repairs; 5, improper extrusion temperature and speed; 6. The product is not straightened before solution treatment; 7. Non-uniform cooling during on-line heat treatment. Prevent method: 1, engage in high mold design, manufacturing level; 2, install the appropriate guide, traction and extrusion; 3. Adjust the metal flow rate with local lubrication, trimming and diversion, or changing diverging orifice design; 4, a reasonable adjustment of extrusion temperature and speed, so that more uniform deformation; 5, appropriate to reduce the temperature of solution treatment or increase the temperature of water used for solution treatment; 6, to ensure uniform cooling when quenched online. Thirteen, hard bend A sudden bend in the length of the extruded product is called a hard bend. Hard bending main causes: 1, the extrusion speed is uneven, from a sudden change to high speed at a low speed, or from a high speed to a sudden change in speed, and sudden stop; 2. Hard moving products in the extrusion process; 3, the work surface of the extruder is uneven. Prevent method: 1. Do not stop or suddenly change the extrusion speed; 2. Do not move the profiles by hand; 3, to ensure that the material out of the material leveling and smoothing out the roller, no foreign body, the product unimpeded. Fourteen, pock This is the surface defect of the extruded product, which means that the surface of the product is fine and uneven, continuous sheet, spot-like abrasion, pitting, metal beans, etc. The main causes of pockmark: 1, mold hardness is not enough or soft and uneven; 2, extrusion temperature is too high; 3, extrusion speed is too fast; 4, mold work with too long, rough or sticky metal; 5, squeezing wool is too long. Prevent method: 1. Improve mold work with hardness and hardness uniformity; 2, according to the regulations heating the extrusion tube and ingot, using the appropriate extrusion speed; 3, rational design mold, reduce the surface roughness of the work zone, strengthen the surface inspection, repair and polishing; 4, using a reasonable length of ingot.