Aluminum alloy materials are widely used by auto parts die-casting enterprises as one of lightweight materials for automobiles on the market. Quality of aluminum alloy die castings will be affected by various factors in actual production process. We will share with you a technical article "Comprehensive Problems and Solutions of Aluminum Alloy Die Casting", hoping that die casting people in the industry can help!

 

(1) Features:
① Line-like strain marks on the surface of casting along mold opening direction, with a certain depth, and in severe cases, the entire surface is strained;
② Molten metal sticks to the surface of mold, resulting in a lack of material on the surface of casting.
(2) Causes:
① Surface of mold cavity is damaged;
② There is no slope or slope is too small in the direction of mold release;
③ Extrusion imbalance;
④ loose mold;
⑤ Casting temperature is too high or too low, and mold temperature is too high to cause alloy liquid to adhere;
⑥ Effect of release agent is not good;
⑦ Iron content of aluminum alloy composition is less than O.8%; cooling time is too long or too short.
(3) Processing method:
① Repair mold surface damage
② Correct slope and improve surface finish of mold
③ Adjust ejector rod to balance ejector force
④ Fasten mold
⑤ Control reasonable casting temperature and mold temperature 180-250
⑥ Replace release agent
⑦ Adjust iron content of aluminum alloy
⑧ Adjust cooling time
⑨ Modify gate and change direction of aluminum liquid.

(1) Features:
Surface of casting has a cavity formed under raised skin of size of a rice grain.
(2) Causes
① Filling of alloy liquid in pressure chamber is too low, which is easy to generate air entrainment, and injection speed is too high;
② Mold is not exhausted;
③ Melt is not degassed, and melting temperature is too high;
④ Mold temperature is too high, and metal solidification time is not enough , strength is not enough, mold is opened prematurely to eject casting, and pressurized gas expands;
⑤ Too much release agent;
⑥ Inner gate is poorly opened, and filling direction is handed over.
(3) Processing method
① Change diameter of small pressure chamber to increase fullness of molten metal;
② Extend injection time, reduce injection speed in the first stage, and change switching point between low-speed and high-speed injection;
③ Reduce mold temperature to maintain heat balance;
④ Add exhaust grooves, Overflow tank, fully exhaust, timely remove oil and waste on exhaust tank_;
⑤ Adjust melting process, and perform degassing treatment;
⑥ Prolong mold retention time appropriately;
⑦ Reduce amount of release agent.

(1) Features:
① Surface of casting has linear or wavy lines, which are narrow and long, and has a tendency to develop under action of external force;
② Metal at crack of cold crack is not oxidized;
③ Metal at crack of hot crack has been oxidized.
(2) Causes:
① Iron content in alloy is too high or silicon content is too high;
② Content of harmful impurities in He Fu is too high, which reduces plasticity of alloy;
③ Al-Si-Cu alloy with too high zinc content or too low copper content;
④ Mold, especially the overall temperature of mold cavity is too low;
⑤ Shrinkage is hindered at places where wall thickness and thinness of castings change drastically, and stress is formed at sharp corners;
⑥ Mold stay time is too long and stress is large;
⑦ Force is uneven when ejecting.
(3)  Processing method:
① Correct control of alloy composition, in some cases, pure aluminum ingots can be added to alloy to reduce magnesium content in alloy or an aluminum-silicon intermediate alloy can be added to aluminum alloy to increase silicon content;
② Change casting structure, add angles, change draft angle, and reduce difference in wall thickness;
③ Change or increase ejection position to make ejection force uniform;
④ Shorten mold opening and core pulling time to increase mold temperature and maintain thermal balance of mold.

 

(1) Features:
① Overall deformation or local deformation;
② Geometric shape of die-casting parts does not match drawings.
(2) Causes:
① Poor casting structure;
② Mold is opened too early, and rigidity of casting is not enough
③ Improper setting of ejector rod, uneven force during ejection;
④ Position of gate or thickness of gate is too thick, and it is easy to deform when gate is removed;
⑤ Rough local surface of mold causes large resistance, and product deforms when it is ejected; if local temperature of mold is too high, product is not fully cured, and force is large when ejected, causing product to deform.
(3) Handling method:
① Improve casting structure;
② Reasonably adjust holding pressure and mold opening date
③ Reasonably set ejection position and number of ejector pins, preferably 4, in an open place; ④ Change gate position so that gate has a point and reduce thickness of gate. To ensure casting quality of product, product will not be easily deformed when gate is removed;
⑤ Strengthen mold surface treatment to reduce demoulding resistance;
⑥ Control local mold temperature to maintain thermal balance of mold.

(1) Features:
There are stripes on the surface of casting that are consistent with flow direction of molten metal, there are obviously non-directional lines that are different in color from metal matrix, and there is no development trend.
(2) Causes:
① Molten metal that first enters cavity forms a very thin and incomplete metal layer, which is left behind by subsequent liquid metal;
② Mold temperature is too low and mold temperature is uneven:
③ Cross-sectional area of inner runner is too small and position is improper to cause splashing;
④ Insufficient pressure acting on molten metal;
⑤ Pattern: Too much paint is used.
(3) Processing method:
① Increase temperature of molten metal by 620℃~650℃;
② Increase mold temperature and maintain a heat balance of 200℃-250℃;
③ Thicken cross-sectional area of inner runner to change inlet position;
④ Adjust filling speed and injection time stroke length;
⑤ Select appropriate paint and adjust contrast concentration dosage.

(1) Features
Surface of die-casting parts has obvious, irregular, and sunken linear lines (there are two kinds of penetration and non-penetration). Shape is small and narrow, and some of junction edges are smooth.
(2) Causes:
① Two metal streams are butted against each other, but they are not completely fused and there is no inclusion in between, and bonding force of the two metal streams is very weak;
② Pouring temperature or die-casting mold temperature is low;
③ Improper selection of alloy, poor fluidity;
④ Position of sprue is wrong or flow path is too long;
⑤ Filling speed is low and injection ratio is low.
(3) Processing method:
① Properly increase pouring temperature and mold temperature;
② Increase injection specific pressure and shorten filling time;
③ Increase injection speed and increase cross-sectional area of gate at the same time;
④ Improve exhaust and filling conditions;
⑤ Correctly select alloy to improve fluidity of alloy.

(1) Features:
Different colors and spots appear on casting surface.
(2) Causes:
Unsuitable release agent in castings, too much release agent, after amount of stone in system falls into the surface of special part, excessive ground irrigation, local accumulation, regular solidification containing graphite, causing temperature of molten metal to be too low.
(3) Processing method:
① Replace high-quality release agent;
② Strict spraying amount and spraying operation;
③ Control mold temperature to maintain thermal balance;
④ Control temperature of molten metal.

(1) Features:
Surface of die-casting part is constantly enlarged and extended due to mesh plus. Just like evolution of protruding gauges, die-casting times box
(2) Causes:
① Cracks on the surface of die-casting mold cavity;
② Improper die-casting mold material or incorrect heat treatment process,
③ Temperature difference between hot and cold of die-casting mold varies greatly; "Because remark temperature is too high, preheating of die-casting mold is insufficient, and surface of round cavity is rough.
(3) Processing method:
① Correct selection of die-casting molds and heat treatment, especially high-field alloys,
② Mold preheating and replacement of heat treatment processes,
③ Pouring temperature should not be too high, but more fully,
④ After mold is manufactured, carry out low-temperature long-term aging treatment or chemical oxidation treatment on the surface;
⑤ Grinding surface of forming part to reduce surface roughness Ra value, Ra0. 8~Ra0. 4;
⑥ Reasonable selection of mold cooling methods;

(1) Features:
Depressions appear on smooth surface of casting.
(2) Causes:
① Wall thickness of castings varies too much, and most of depressions occur at thick wall;
② Mold is partially overheated, and overheated part solidifies slowly;
③ Injection pressure is low;
④ Gas in cavity cannot be discharged due to high temperature of mold, and it is compressed on the surface of cavity between interface with molten metal.
(3) Processing method:
① Wall thickness of casting is designed to be as uniform as possible;
② Local cooling of mold is adjusted;
③ Injection specific pressure is increased;
④ Cavity exhaust condition is improved.

 

(1) Features:
There are insufficient pouring parts on the surface of casting; outline is not clear.
(2) Causes:
① Reasons for poor fluidity;
② Alloy liquid absorbs air, oxidizes inclusions, and high iron content, which makes its quality poor and reduces fluidity;
③ Low pouring temperature or low mold temperature;
④ Poor filling conditions;
⑤ Low specific pressure;
⑥ Too much gas is involved, back pressure of cavity becomes higher, and filling is blocked;
⑦ Operation is poor, paint is excessively sprayed, paint is accumulated, and gas cannot be volatilized.
(3) Processing method:
① Improve quality of alloy liquid;
② Increase pouring temperature or mold temperature;
③ Increase specific pressure and filling speed;
④ Improve diversion mode of molten metal in gating system, add overflow grooves and exhaust grooves in undercast parts;
⑤ Check whether capacity of die casting machine is sufficient

(1) Features:
Die castings have metal flakes on the edge of parting surface.
(2) Causes:
① Insufficient mold clamping;
② Injection speed is too high, resulting in a high pressure shock peak;
③ Debris on parting surface is not cleaned;
④ Insufficient mold strength causes deformation;
⑤ Insert, slider wear and parting uneven.
(3) Processing method:
① Check mold clamping force and pressurization, adjust die-casting process parameters;
② Clean cavity and parting surface;
③ Repair mold;
④ It is best to use a closed injection end time control system to achieve flash-free die-casting.

(1) Features and inspection methods:
Visual inspection or flaw detection after dissection, stomata have a smooth surface and are circular in shape.
(2) Causes:
① Direction of introduction of alloy liquid is unreasonable or flow rate of metal liquid is too high, resulting in jetting;
② Exhaust channel is blocked prematurely or front impacts wall to form a vortex to enclose air. Such pores are mostly generated in poor exhaust or deep cavities;
③ Because charge is not clean or smelting temperature is too high, more gas in molten metal is not removed, it precipitates during solidification and cannot be fully discharged;
④ Paint has a large amount of gas generation or is used too much, and it is not poured before pouring, so that gas is involved in casting, and gas is mostly dark gray on the surface; high-speed switching point is wrong.
(3) Processing method:
① Use clean charge, control melting temperature, and perform exhaust treatment;
② Select reasonable process parameters, injection speed, and high-speed switching point;
③ Guide pressure balance of metal liquid, fill cavity in an orderly manner, and facilitate gas discharge;
④ Exhaust grooves and overflow grooves must have sufficient exhaust capacity;
⑤ Choose a paint with a small gas generation and control exhaust volume.

(1) Features and inspection methods:
① Dissection or flaw detection inspection, shape of holes is irregular, not smooth, and surface is dark;
② Large and concentrated shrinkage holes are small and scattered shrinkage porosity.
(2) Causes:
① During solidification process of casting, holes are caused due to shrinkage and lack of metal compensation;
② Pouring temperature is too high, and distribution of mold temperature gradient is unreasonable;
③ Injection specific pressure is low, and boost pressure is too low;
④ Inner gate is thin, area is too small, premature solidification, which is not conducive to pressure transmission and metal liquid feeding;
⑤ There are hot joints or cross-sections in casting structure that change drastically;
⑥ Pouring amount of molten metal is too small, and remaining material is too thin to achieve feeding effect.
(3) Processing method:
① Reduce pouring temperature to reduce shrinkage;
② Increase injection specific pressure and boost pressure to improve compactness;
③ Modify inner gate to make pressure better transfer, which is beneficial to liquid metal feeding effect;
④Change casting structure, eliminate metal accumulation parts, and make wall thickness as uniform as possible;
 ⑤ Speed up cooling of thick and large parts;
⑥ Thicken material handle by 15~30mm to increase effect of shrinkage.

(1) Features and inspection methods:
Metallic or non-metallic impurities mixed into die-casting, after processing, irregular states, points or holes with different sizes, colors and heights can be seen.
(2) Causes:
① Furnace material is not clean, and there are too many returned materials;
② Alloy liquid is not refined;
③ Slag is brought in when liquid is poured with a spoon;
④ Graphite crucible or coating contains graphite falling off and mixed into metal liquid;
⑤ Temperature is high during heat preservation, and duration long.
(3) Processing method:
① Use clean alloy materials, especially dirt on returned materials must be cleaned;
② Alloy melt must be refined and degassed, and slag should be cleaned;
③ When pouring with a spoon, carefully remove liquid surface to avoid mixing slag and scale;
④ Clean cavity, pressure chamber;
⑤ Control holding temperature and reduce holding time.

 

(1) Features and inspection methods:
Metal grains of casting matrix are too thick or extremely small, which makes casting easy to break or shatter.
(2) Causes:
① Impurities zinc, iron, lead, and tin in aluminum alloy exceed specified range;
② Alloy liquid is overheated or holding time is too long, resulting in coarse grains;
③ Intense supercooling makes grains too fine.
(3) Processing method:
① Strictly control impurity components in metal;
② Control smelting process and reduce pouring temperature;
③ Increase mold temperature.

(1) Features and inspection methods:
After pressure test, die castings have air leakage and water seepage.
(2) Causes:
① Insufficient pressure, poor density of matrix structure;
② Caused by internal defects, such as pores, shrinkage cavities, slag holes, cracks, shrinkage porosity, cold septa, patterns;
③ Poor design of pouring and exhaust systems;
④ Die-casting punch wear, pressure Ejaculation is unstable.
(3) Processing method:
① Increase specific pressure;
② Take corresponding measures for internal defects;
③ Improve pouring system and exhaust system;
④ Perform impregnation treatment to make up for defects;
⑤ Replace pressure chamber and punch.

(1) Features and inspection methods:
During mechanical processing or post-processing visual inspection or metallographic inspection, it is found that there are small particles or lumps on casting that have a hardness higher than that of metal matrix, which causes severe tool wear, and often shows different brightness after processing.
(2) Causes:
① Non-metallic hard spots;
② Mixed with oxides on the surface of alloy liquid;
③ Reactant between aluminum alloy and furnace lining;
④ Metal material sneaking into foreign matter;
⑤ inclusions.
(3) Processing method:
① Do not scoop oxides on the surface of alloy liquid into spoon during casting;
② After removing oxides on the surface of iron crucible, paint it. Clean up residue on furnace wall and furnace bottom in time;
③ Remove oxides on spoons and other tools;
④ Use furnace lining materials that do not react with aluminum;
⑤ Pure metal materials.

(1) Features and inspection methods:
During mechanical processing or post-processing visual inspection or metallographic inspection, it is found that there are small particles or lumps on casting that have a hardness higher than that of metal matrix, causing serious tool wear, and often show different brightness after processing.
(2) Causes:
① Metal hard spots are mixed with unmelted silicon elements;
② Primary silicon: temperature of molten aluminum is low, and parking time is long;
③ FE and MN elements segregate to produce intermetallic compounds.
(3) Processing method:
① When smelting aluminum-silicon alloy, do not use silicon element powder;
②When high-speed alloy composition, do not directly add silicon element, must use intermediate alloy;
③ Increase melting temperature and pouring temperature;
④ Control alloy composition, especially FE impurity amount; avoid FE, MN and other elements segregate;
⑤ Amount of Si in alloy should not be close to or exceed eutectic composition;
⑥ Amount of primary silicon in matrix metallographic structure should be controlled for raw materials.

Since cause of each defect comes from many different influencing factors, in order to solve problem in actual production, in the face of many reasons, should we adjust machine first? Or repair mold first?
It is recommended to deal with it according to degree of difficulty, first simple and then complex, in order:
(1) Clean parting surface, clean cavity, clean ejector pin; change coating, improve spraying process; increase clamping force; increase amount of pouring metal; these are measures that can be implemented by simple operations.
(2) Adjust process parameters, injection force, injection speed, filling time, mold opening time, pouring temperature, mold temperature, etc.
(3) Refueling, selecting high-quality alloy ingots, changing ratio of new materials to recycled materials, and improving smelting process.
(4) Modify mold, modify gating system, increase gate, add overflow grooves, exhaust grooves, etc.

 

(1) Die casting machine problems:
Clamping force is not adjusted correctly.
(2) Technological issues:
Injection speed is too high, and pressure shock peak is too high.
(3) Mold problem:
Deformation, debris on parting surface, wear and tear on inserts and sliders, and insufficient template strength.
(4) Order of measures to solve flash:
1. Clean parting surface
2. Improve clamping force
3. Adjust process parameters
4. Repair worn part of mold
5. Improve rigidity of mold.