GB/T 25745-2010Heat treatment of cast aluminium alloys (English PDF)

5.1 Heating equipment

5.1.1 Generally, an air circulation resistance heating furnace with a fan shall be used for the heat treatment of cast aluminium alloys, or a fuel furnace can be used to heat by the gas generated by combustion or a gas radiant tube. Direct heating of the flame is prohibited; measures such as setting a heat shield are used to prevent direct heating of the workpiece.

5.1.5 The temperature measurement system used on site shall be regularly subjected to system check under normal use. During the check, the distance between the detection thermocouple and the hot end of the recording instrument thermocouple shall be close.

The check shall be performed with the furnace in a thermal stability.

5.2 Temperature control equipment

5.2.1 The accuracy of the on-site testing equipment shall be higher than that of the tested equipment.

5.2.4 Mercurial thermometer for measuring room temperature, with a resolution of 0.1°C and a verification cycle of 1 year.

5.2.5 The thermocouple shall comply with the provisions of GB/T 16839.2. See Table 5 for the technical requirements for the thermocouple commonly used on site.

5.3 Solid solution cooling tank

5.3.1 The solid solution cooling tank shall be located as close to the heating furnace as possible, so as to ensure that the heated castings are quickly immersed in the solid solution cooling tank; the solid solution cooling transfer time shall meet the requirements in Table 5.

6.1 Preparation before heat treatment

6.1.1 Check the conditions of the heating furnace, temperature control equipment, solid solution cooling tank, etc. before use, to ensure that the equipment is in good condition.

6.2 Furnace loading

6.2.1 Load according to the classification of the alloy designations, the geometric dimensions of castings and the heat treatment system.

6.2.2 Castings shall be installed in the effective working area of the heating furnace.

6.3 Heat treatment system

6.3.1 The temperature for solid solution treatment of aluminium alloy castings shall meet the requirements in Table 5.

6.3.3 When castings of different thicknesses are installed in the same heat treatment furnace, the heating and holding time shall be determined according to the maximum thickness. The holding time is calculated from the time when the lowest temperature recording thermocouple in the working area of the heating equipment reaches the lower limit of the specified temperature.

6.3.7 The time of the casting in the solid solution cooling medium shall be determined based on the maximum thickness of the casting, but shall not be less than 2 min.

6.3.8 Castings with higher requirements on dimensional accuracy and dimensional stability can be subjected to cold-heat circulating treatment (T9) as specified in Table 6. The specific process is as follows. […]

6.4 Repeated heat treatment

6.4.1 When the mechanical property of the casting after heat treatment is unqualified, a repeated heat treatment can be performed; the holding time of the repeated heat treatment can be reduced according to the circumstances; the times of repetition of solution treatment shall not exceed two times in general; the times of repetition of the aging treatment is not limited.

7.1 Quality control

7.1.1 Personnel requirements

Heat treatment operators, instrument staff, and inspectors shall be trained according to regulations, and they can take up their posts after passing the examination and obtaining the qualification certificate.

7.1.2 Heat treatment process control

7.1.3 Record

7.2 Inspection

7.2.1 Appearance inspection

Castings after heat treatment shall be free of cracks, surface blistering, oxidation blackening and deformation.

The appearance inspection shall be carried out visually (or with a magnifying glass below 10 times).

7.2.4 Metallographic examination

The metallographic structure after heat treatment is not allowed to have over-burned structure.