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    • 铝合金铸造的工艺性能有哪些?
    • 本站编辑:杭州宏成精密机械有限公司发布日期:2018-05-17 16:23 浏览次数:
    铝合金铸造工艺性能,通常理解为在充满铸型、结晶和冷却过程中表现比较为突出的那些性能的综合。流动性、收缩性、气密性、铸造应力、吸气性。铝合金这些特性取决于合金的成分,但也与铸造因素、合金加热温度、铸型的复杂程度、浇冒口系统、浇口形状等有关。
    The casting process performance of aluminum alloys is generally understood as the synthesis of those properties that are most outstanding in mold filling, crystallization and cooling. Liquidity, shrinkage, air tightness, casting stress and inhalation. These properties depend on the composition of the alloy, but it is also related to the casting factors, the heating temperature of the alloy, the complexity of the mold, the pouring and riser system, the shape of the gate and so on.




    一、流动性
    1. Liquidity
    流动性是指合金液体充填铸型的能力。流动性的大小决定合金能否铸造复杂的铸件。在铝合金中共晶合金的流动性比较好。
    Liquidity refers to the ability of alloy liquid filling mold. The size of fluidity determines whether the alloy can cast complex castings. The fluidity of the eutectic alloy in aluminum alloy is the best.
    影响流动性的因素很多,主要是成分、温度以及合金液体中存在金属氧化物、金属化合物及其他污染物的固相颗粒,但外在的根本因素为浇注温度及浇注压力(俗称浇注压头)的高低。
    There are many factors affecting the fluidity, mainly components, temperatures and solid particles of metal oxides, metal compounds and other pollutants in the composition, temperature and alloy liquids, but the external factors are the pouring temperature and the pouring pressure (commonly known as the pouring pressure head).
    实际生产中,在合金已确定的情况下,除了强化熔炼工艺(精炼与除渣)外,还必须改善铸型工艺性(砂模透气性、金属型模具排气及温度),并在不影响铸件质量的前提下提高浇注温度,保证合金的流动性。
    In actual production, in addition to strengthening the smelting process (refining and slag removal), it is necessary to improve the casting technology (sand mold permeability, metal mold exhaust and temperature), and improve the pouring temperature without affecting the quality of the castings to ensure the fluidity of the alloy.
    二、收缩性
    Two, contractility
    收缩性是铸造铝合金的主要特征之一。一般讲,合金从液体浇注到凝固,直至冷到室温,共分为三个阶段,分别为液态收缩、凝固收缩和固态收缩。合金的收缩性对铸件质量有决定性的影响,它影响着铸件的缩孔大小、应力的产生、裂纹的形成及尺寸的变化。通常铸件收缩又分为体收缩和线收缩,在实际生产中一般应用线收缩来衡量合金的收缩性。铝合金收缩大小,通常以百分数来表示,称为收缩率。
    Shrinkage is one of the main characteristics of cast aluminum alloy. Generally speaking, alloy pouring from liquid to solidification, until cold to room temperature, is divided into three stages, namely liquid shrinkage, solidification shrinkage and solid shrinkage. The shrinkage of the alloy has a decisive influence on the casting quality, which affects the size of shrinkage cavity, the generation of stress, the formation of cracks and the change of size. Usually shrinkage of casting is divided into body contraction and linear shrinkage. In practice, linear shrinkage is used to measure shrinkage of alloy. The shrinkage of aluminum alloy is usually expressed as a percentage, which is called shrinkage.
    1、体收缩 体收缩包括液体收缩与凝固收缩。
    1. Contraction of body contractile includes liquid contraction and solidification contraction.
    铸造合金液从浇注到凝固,在比较后凝固的地方会出现宏观或显微收缩,这种因收缩引起的宏观缩孔肉眼可见,并分为集中缩孔和分散性缩孔。集中缩孔的孔径大而集中,并分布在铸件顶部或截面厚大的热节处。分散性缩孔形貌分散而细小,大部分分布在铸件轴心和热节部位。显微缩孔肉眼难以看到,显微缩孔大部分分布在晶界下或树枝晶的枝晶间。
    From casting to solidification, the casting alloy liquid will have macroscopic or microscopic contraction in the place of final solidification, which is visible to the macroscopic shrinkage cavity caused by contraction and is divided into concentrated shrinkage and dispersive shrinkage. The concentric shrinkage hole is large and concentrated, and is distributed at the top of the casting or the hot section with thick section. The dispersed shrinkage cavity is dispersed and small, mostly distributed in the center of the casting and the hot spot. Microscopic shrinkage holes are hard to see. Most of the Microshrinkage holes are distributed between grain boundaries or dendrites.
    缩孔、疏松是铸件的主要缺陷之一,产生的原因是液态收缩大于固态收缩。生产中发现,铸造铝合金凝固范围越小,越易形成集中缩孔,凝固范围越宽,越易形成分散性缩孔,因此,在设计中必须使铸造铝合金符合顺序凝固原则,即铸件在液态到凝固期间的体收缩应得到合金液的补充,是缩孔和疏松集中在铸件外部冒口中。对易产生分散疏松的铝合金铸件,冒口设置数量比集中缩孔要多,并在易产生疏松处设置冷铁,加大局部冷却速度,使其同时或快速凝固。
    Shrinkage porosity and porosity are one of the main defects of castings. The reason is that liquid shrinkage is greater than solid shrinkage. It is found that the smaller the solidification range of the cast aluminum alloy is, the more the concentrated shrinkage cavity is formed, the wider the solidification range is, the more easily the dispersing shrinkage is formed. Therefore, the casting aluminum alloy must be in accordance with the principle of sequential solidification in the design, that is, the shrinkage of the castings in the period of liquid to solidification should be supplemented to the alloy liquid, which is the shrinkage and porosity. It is concentrated in the outer risers of the castings. For the easily produced and loose and loose aluminum alloy castings, the number of risers is more than the concentrated shrinkage hole, and cold iron is set in the loose place, and the local cooling speed is increased so that it can solidify at the same time or quickly.
    2、线收缩 线收缩大小将直接影响铸件的质量。线收缩越大,铝铸件产生裂纹与应力的趋向也越大;冷却后铸件尺寸及形状变化也越大。
    2, the shrinkage of linear shrinkage will directly affect the quality of castings. The larger the linear shrinkage, the greater the tendency of crack and stress in aluminum castings, and the bigger the size and shape of the castings after cooling.
    对于不同的铸造铝合金有不同的铸造收缩率,即使同一合金,铸件不同,收缩率也不同,在同一铸件上,其长、宽、高的收缩率也不同。应根据具体情况而定。
    There are different shrinkage rates for different cast aluminum alloys. Even the same alloy, the casting is different, and the shrinkage rate is different. In the same casting, the shrinkage rate of the same casting is different. It should be determined according to the specific circumstances.
    三、热裂性
    Three. Thermal cracking
    铝铸件热裂纹的产生,主要是由于铸件收缩应力超过了金属晶粒间的结合力,大多沿晶界产生从裂纹断口观察可见裂纹处金属往往被氧化,失去金属光泽。裂纹沿晶界延伸,形状呈锯齿形,表面较宽,内部较窄,有的则穿透整个铸件的端面。
    The thermal cracking of aluminum castings is mainly due to the shrinkage stress of the castings, which is more than the binding force between the metal grains. Most of the metals tend to be oxidized at the crack fracture surface along the grain boundary, and the metal luster is lost. The crack extends along the grain boundary, the shape is zigzag, the surface is wider, the inside is narrow, and others penetrate the whole casting end face.
    不同铝合金铸件产生裂纹的倾向也不同,这是因为铸铝合金凝固过程中开始形成完整的结晶框架的温度与凝固温度之差越大,合金收缩率就越大,产生热裂纹倾向也越大,即使同一种合金也因铸型的阻力、铸件的结构、浇注工艺等因素产生热裂纹倾向也不同。生产中常采用退让性铸型,或改进铸铝合金的浇注系统等措施,使铝铸件避免产生裂纹。通常采用热裂环法检测铝铸件热裂纹。
    The tendency of different aluminum alloy castings to produce cracks is also different. This is because the greater the difference between the temperature and the solidification temperature, the greater the shrinkage of the alloy and the greater the tendency to produce hot cracks. Even the same alloy is also due to the cast resistance, the structure of the casting, and the castable. The tendency of producing hot cracks is also different. In order to avoid cracks in aluminum castings, measures such as concession mold or gating system for casting aluminum alloy are often adopted. Hot cracking method is usually used to detect hot cracks in aluminum castings.
    四、气密性
    Four. Air tightness
    铸铝合金气密性是指腔体型铝铸件在高压气体或液体的作用下不渗漏程度,气密性实际上表征了铸件内部组织致密与纯净的程度。
    The gas tightness of cast aluminum alloy refers to the non leakage degree of aluminum castings under the action of high pressure gas or liquid, and the air tightness actually characterizing the density and purity of the internal structure of the castings.
    铸铝合金的气密性与合金的性质有关,合金凝固范围越小,产生疏松倾向也越小,同时产生析出性气孔越小,则合金的气密性就越高。同一种铸铝合金的气密性好坏,还与铸造工艺有关,如降低铸铝合金浇注温度、放置冷铁以加快冷却速度以及在压力下凝固结晶等,均可使铝铸件的气密性提高。也可用浸渗法堵塞泄露空隙来提高铸件的气密性。
    The gas tightness of the cast aluminum alloy is related to the properties of the alloy. The smaller the solidification range of the alloy is, the smaller the porosity is, the smaller the precipitating porosity is, the higher the gas tightness of the alloy. The gas tightness of the same cast aluminum alloy is also related to the casting process, such as reducing the casting temperature of cast aluminum alloy, placing cold iron in order to speed up cooling rate and solidification crystallization under pressure, which can improve the air tightness of aluminum casting. The leakage gap can also be blocked by impregnation to improve the tightness of the castings.
    五、.铸造应力
    Five. Casting stress
    铸造应力包括热应力、相变应力及收缩应力三种。各种应力产生的原因不尽相同。
    Casting stress includes three kinds: thermal stress, phase transformation stress and shrinkage stress. The causes of all kinds of stress are not the same.
    1、热应力 热应力是由于铸件不同的几何形状相交处断面厚薄不均,冷却不一致引起的。在薄壁处形成压应力,导致在铸件中残留应力。
    1, thermal stress and thermal stress are caused by uneven thickness and uneven cooling at different cross sections of castings. Compressive stress is formed at the thin wall, resulting in residual stress in the casting.
    2、相变应力 相变应力是由于某些铸铝合金在凝固后冷却过程中产生相变,随之带来体积尺寸变化。主要是铝铸件壁厚不均,不同部位在不同时间内发生相变所致。
    2, phase transformation stress transformation stress is due to phase transformation of some cast aluminum alloys during cooling process, resulting in volume size changes. It is mainly due to uneven wall thickness of aluminum castings, and phase transformation occurs at different locations at different times.
    3、收缩应力 铝铸件收缩时受到铸型、型芯的阻碍而产生拉应力所致。这种应力是暂时的,铝铸件开箱是会自动消失。但开箱时间不当,则常常会造成热裂纹,特别是金属型浇注的铝合金往往在这种应力作用下容易产生热裂纹。
    3, shrinkage stress aluminum casting shrinkage caused by mold and core obstruction caused by tensile stress. This kind of stress is temporary, and the casting of aluminum castings will disappear automatically. But the improper opening time often leads to thermal cracks, especially when the metal mold cast aluminum alloys are prone to produce hot cracks under such stress.
    铸铝合金件中的残留应力降低了合金的力学性能,影响铸件的加工精度。铝铸件中的残留应力可通过退火处理消除。合金因导热性好,冷却过程中无相变,只要铸件结构设计合理,铝铸件的残留应力一般较小。
    The residual stress in the cast aluminum alloy reduces the mechanical properties of the alloy and affects the machining accuracy of the casting. Residual stresses in aluminum castings can be eliminated by annealing treatment. Because of the good thermal conductivity and no phase transformation in the cooling process, the residual stress of the aluminum castings is generally small as long as the structural design of the casting is reasonable.
    六、吸气性
    Six, inhalation
    铝合金易吸收气体,是铸造铝合金的主要特性。液态铝及铝合金的组分与炉料、有机物燃烧产物及铸型等所含水分发生反应而产生的氢气被铝液体吸收所致。
    Aluminum alloy is easy to absorb gas and is the main characteristic of casting aluminum alloy. The composition of liquid aluminum and aluminum alloy is reacted with the water contained in the burden, burning products and mould of organic matter, and the hydrogen generated is absorbed by aluminum liquid.
    铝合金熔液温度越高,吸收的氢也越多;在700℃时,每100g铝中氢的溶解度为0.5~0.9,温度升高到850℃时,氢的溶解度增加2~3倍。当含碱金属杂质时,氢在铝液中的溶解度显著增加。
    The higher the temperature of the molten aluminum is, the more hydrogen is absorbed. At 700, the solubility of hydrogen in every 100g aluminum is 0.5 to 0.9, and the solubility of hydrogen is increased by 2~3 times when the temperature rises to 850. When alkali metal impurities are added, the solubility of hydrogen in aluminum solution increases significantly.
    铸铝合金除熔炼时吸气外,在浇入铸型时也会产生吸气,进入铸型内的液态金属随温度下降,气体的溶解度下降,析出多余的气体,有一部分逸不出的气体留在铸件内形成气孔,这就是通常称的“针孔”。气体有时会与缩孔结合在一起,铝液中析出的气体留在缩孔内。若气泡受热产生的压力很大,则气孔表面光滑,孔的周围有一圈光亮层;若气泡产生的压力小,则孔内表面多皱纹,看上去如“苍蝇脚”,仔细观察又具有缩孔的特征。
    In addition to the inhalation of the cast aluminum alloy, the cast aluminum alloy will also breathe in when pouring into the mold, and the liquid metal entering the mold drops with the temperature, the solubility of the gas drops, the excess gas is precipitated, and a part of the gas is left in the casting to form the air hole, which is the commonly called "pinhole". Sometimes the gas will be combined with the shrinkage hole, and the gas in the molten aluminum will remain in the shrinkage cavity. If the pressure of the bubble is hot, the surface of the hole is smooth and there is a ring of light around the hole. If the pressure is small, the inner surface of the hole is wrinkled, it looks like the "fly foot", and it is carefully observed and has the characteristics of shrinkage.
    铸铝合金液中含氢量越高,铸件中产生的针孔也越多。铝铸件中针孔不仅降低了铸件的气密性、耐蚀性,还降低了合金的力学性能。要获得无气孔或少气孔的铝铸件,关键在于熔炼条件。若熔炼时添加覆盖剂保护,合金的吸气量大为减少。对铝熔液作精炼处理,可有效控制铝液中的含氢量。
    The higher the hydrogen content in the molten aluminum alloy, the more pinholes produced in the casting. Pinholes in aluminum castings not only reduce the air tightness and corrosion resistance of the castings, but also reduce the mechanical properties of the alloys. The key to obtain aluminum castings without air holes or small pores is melting conditions. If the covering agent is added to protect the alloy, the suction volume of the alloy will be greatly reduced. Refining of aluminum melt can effectively control the amount of hydrogen contained in molten aluminum.