Eliminate the common defects of heat treatment and prevention technology

Defect name defect causes to eliminate performance and mechanical properties to prevent unqualified 5 low annealing state delta, quenching or aging treatment after the strength and elongation is unqualified. Low annealing temperature or holding time is insufficient, or cooling fast; Quenching temperature is low or the holding time is not enough, or too slow cooling ( Quenching medium high temperature) ; Incomplete artificial aging and artificial aging temperature on the high side, completely or partial long time of heat preservation, the chemical composition of alloy appeared deviation. Annealing again, raising temperature or extended holding time; Improve quenching temperature or extended holding time, decrease the temperature of quenching medium; Such as quenching, again is to adjust the following ageing temperature and time; Such as composition appeared deviation, according to the specific elements of deviation, deviation value, change or adjust the repeated heat treatment parameters. After heat treatment deformation, warping, or after machining is reflected in the size and shape changes of castings. Heating speed or quenching cooling rate is too fast, Too intense) ; Quenching temperature is too high; The design of the casting structure is not reasonable, Such as the huge difference between two connected to the wall thickness, frame structure reinforcing rib is too thin or too small; When quenching water direction and improper loading method. Reduce speed, improving temperature of quenching medium, or for cooling the slower quenching medium in order to prevent the residual stress produced in alloy; In the thick wall or thin wall parts coated paint or use the insulation coating thin wall parts such as asbestos fibers; Choice of the reasonable water direction according to the casting structure, appearance, or use of preventing deformation fixture; Parts of the deformation is, can be corrected immediately after quenching. Crack after hardening of the surface of the casting with the naked eye can see obvious flaw or by fluoroscopy microcrack is invisible to the naked eye. Many twists and turns of crack is not straight and dark grey. When heating speed is too fast, quenching cooling fast ( Quenching temperature too high or medium quenching temperature is too low, or quenching medium too fast) ; Casting structure design is not reasonable, Two connecting wall thickness difference is too big, box shaped parts in the middle of the reinforcing rib is too thin or too small) ; Improper furnace charging method or water right direction; Uneven uneven temperature, make the casting temperature. To slow down the speed or adopts the isothermal quenching process; Elevating the temperature of the quenching medium or replaced by slow cooling of quenching medium; In wall thickness or thin wall parts coated paint or in thin wall parts coating such as asbestos insulation materials; Using special anti cracking quenching fixture and choose the correct direction of the water. Burnt with nodular casting surface, an extension of the alloy rate drops greatly. Low melting point impurity in the alloy elements such as Cd, high content of Si, Sb, etc; Uneven heating or heating fast; The local temperature in the furnace over burnt temperature of the alloy; Temperature measurement and control instrument malfunction, make the temperature more than the actual temperature instrument. Strictly control the content of low melting point alloy elements not overweight; With no more than 3 ℃ / min speed slow warming; Check and control districts in the furnace temperature is not more than + / - 5 ℃; Regular inspection or calibration measurement and control instruments, to ensure that the instrument temperature measurement, temperature, temperature control is accurate. Surface corrosion casting surface markings or block with different color on the surface of the aluminum alloy castings. Excessive nitrate chloride content in the liquid> 0. 5%) The surface finish for the castings, Especially osteoporosis, shrinkage) Cause corrosion; From the nitrate slot fully after cleaning, nitrate adhesion on the casting surface ( Especially in narrow gap, blind holes, channel) Cause corrosion; Nitrate in the liquid mixed with acid or alkali or casting in strong acid or strong alkali from corrosion. Try to shorten the casting from furnace to quench tank; Check the excessive content of chloride in nitrate, such as overweight, should reduce its concentration ( Or concentration) From nitrate slot in the heat of the casting shall be immediately rinse off with warm water or cold water; Check the content of nitrate in acid and alkali, such as acid or alkali should be neutral or stop using; Don't put the aluminum alloy castings with strong acid or strong alkali. Quenching uneven thickness of casting large elongation and low hardness ( Especially its internal center) , thin wall parts of high hardness, Especially the surface) 。 Thick castings uneven heating and cooling, most slow cooling, heat through sexual difference. To make heat treatment, reduce the heating rate and prolong the preservation time, make the thickness part temperature equilibrium; In thick walled parts coated insulating heat preservation coating or coating such as asbestos stays material, try to make each part of the casting cooling at the same time; Make the most of thick of38; With organic quenching agent to reduce the cooling rate.