Determination of Cast Aluminum Alloy Corrosion in Engine Coolant

Overview

Engine coolant, also known as antifreeze, is mainly used in automotive engine cooling systems for heat dissipation, freeze protection and boil-over prevention. During actual engine operation, coolant directly contacts cast aluminum alloy components such as aluminum cylinder heads. Under high-temperature heat transfer conditions, insufficient corrosion protection of the coolant will easily cause corrosion of aluminum alloy parts, resulting in pitting corrosion and leakage of cylinder heads and leading to engine failures. Therefore, testing the corrosion performance of coolant against cast aluminum alloy under heat transfer conditions is a key item for evaluating engine coolant quality, and concentrated coolant also requires this corrosion performance assessment.

Experimental Purpose

To determine the corrosion degree of engine coolant (including concentrated solution) on cast aluminum alloy under heat transfer state and evaluate the anti-corrosion performance of the coolant. This test is carried out in accordance with the petrochemical industry standard SH/T 0620 Test Method for Corrosion of Cast Aluminum Alloys by Engine Coolant under Heat Transfer Conditions, and the SH0620 Engine Coolant Cast Aluminum Alloy Corrosion Tester is used to complete the whole test.

Test Samples and Instruments

Test sample: Engine coolant (or its concentrated solution) Test instruments:

1. SH0620 Engine Coolant Cast Aluminum Alloy Corrosion Tester
2. Supporting aluminum test specimens, glass container, thermometer, air inlet hose, silicone sealing gaskets and other accessories

Operating Procedure

1. Prepare the coolant test sample according to the requirements of SH/T 0620 standard. Clean and treat the aluminum specimen, glass container, gaskets, upper and lower end plates thoroughly.
2. Place the aluminum specimen fitted with a large silicone ring at the center of the instrument’s heating base, install the glass container, cover the upper lid equipped with a small silicone ring, tighten the nuts evenly diagonally. The nuts shall be properly tightened and must not be over-tightened.
3. Pour 500 mL of test sample into the heat-transfer corrosion chamber through the air inlet, install the safety guard, mount the sensor and thermometer, connect compressed air and pressurize the chamber to a gauge pressure of 0.14 MPa.
4. Power on the instrument. The PV window of the temperature controller shows the actual bath temperature, and SP represents the set temperature. In this test, the specimen temperature is set to 135 °C. To modify the temperature, press SET to enter the setting interface, select the digit to adjust the temperature parameter, and confirm to exit after setting.
5. Start heating. As the internal chamber temperature rises, the pressure increases synchronously. Continuously adjust the pressure; when the specimen temperature stabilizes at 135 °C, maintain the chamber pressure within 190–200 kPa.
6. Turn on the timer to start test timing. The standard test duration is 168 hours. The timer supports reset and pause functions; the instrument gives a buzzer alarm when timing finishes.
7. Immediately cut off the power after the test ends. Wait until the heat-transfer corrosion chamber cools completely to room temperature, release the internal pressure, disassemble the chamber and take out the aluminum alloy specimen.
8. Clean and weigh the specimen following the SH/T 0620 standard procedure, calculate corrosion loss and compile test results.

Data Analysis and Result Evaluation

This test was conducted for 168 h under the conditions of 135 °C ± 1 °C and 190–200 kPa. The measured mass changes of three parallel cast aluminum alloy specimens were +0.18 mg/cm², +0.21 mg/cm² and +0.19 mg/cm² respectively, with an average mass change of +0.19 mg/cm², which meets the technical requirement of no more than ±1.0 mg/cm². After the test, the precipitate at the bottom of the test solution was 0.02 mL, lower than the standard limit of 0.05 mL. Based on the above data, it can be judged that this engine coolant has qualified protective performance against cast aluminum alloy under heat transfer conditions, can effectively inhibit corrosion of aluminum cylinder heads, and meets the actual operating requirements of engines.

If the specimen mass change exceeds ±1.0 mg/cm² or the solution precipitate exceeds 0.05 mL, it indicates insufficient anti-corrosion performance of the coolant, which carries the risk of corrosion damage to aluminum alloy engine components after application.

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