Aluminum Alloy Door and Window Material Testing

Aluminium alloy door and window material inspection mainly conducts scientific testing and analysis on the chemical composition analysis, mechanical property testing, dimension and geometric tolerance testing, surface treatment property testing, corrosion resistance testing and thermal insulation property testing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Chemical composition analysis: The contents of the main alloying elements and impurity elements such as the silicon, magnesium, manganese, iron and copper in the aluminium alloy are precisely determined through the spectroscopic analysis (such as the spark direct-reading spectrometry). This is the primary step of verifying whether the aluminium alloy designations (such as 6063-T5 and 6061-T6) meet the national standards (such as GB/T 5237.1), directly affecting the mechanical properties and corrosion resistance of the material.

Mechanical property testing: Mainly including the tensile testing, hardness testing and impact testing. The tensile testing determines the tensile strength, specified non-proportional extension strength (Rp0.2) and elongation after fracture, evaluating the load-bearing and deformation abilities of the profiles under the stressed states. The hardness testing (commonly using the Webster hardness testers) quickly detects the local compression resistance of the profiles, and is the key means of the on-site quality control.

Dimension and geometric tolerance testing: The high-precision callipers, micrometers, feeler gauges and coordinate measuring machines, etc. are used to measure the cross-section dimensions, wall thicknesses, angles, plane clearances, straightness and twist of the profiles. The strict dimension control is the basis of ensuring the door and window assembly precision, sealing performance and appearance flatness, and must meet the detailed provisions of GB/T 5237.1.

Surface treatment property testing: For the different surface treatment methods such as the anodizing, electrophoretic coating, powder spraying and fluorocarbon spraying, the film thicknesses (using the eddy current thickness gauges), coating adhesion (cross-cut testing), glossiness, colour differences and corrosion resistance (such as the neutral salt spray testing and CASS testing) are tested. These indicators are directly related to the decorative effects and long-term weather resistance of the door and window.

Corrosion resistance testing: Evaluates the ability of the aluminium alloy material and surface coatings to resist the environmental erosion. The main methods include the neutral salt spray testing (NSS), copper-accelerated acetic acid salt spray testing (CASS) and damp heat resistance testing. Through the simulation of the harsh environments and the acceleration of the aging processes, whether the corrosion, blistering and peeling occur on the specimen surfaces is observed.

Thermal insulation property (thermal conductivity) testing: For the thermal break aluminium profiles, the core testing items are the thermal conductivity of the insulation materials and the overall thermal performance of the composite profiles. Usually, the heat flow meter method or guarded hot plate method is adopted for the testing, to verify their "cold bridge" blocking effects, ensuring that the door and window reach the designed thermal parameters (such as the K values).

Testing Scope

Base materials (aluminium profiles): The testing objects are the aluminium alloy extruded profiles constituting the main bodies such as the door and window frames, sashes, mullions and transoms. The testing covers all the key characteristics of their original states, including the alloy compositions, internal structures, mechanical strengths, dimension precision and straightness, and is the core of ensuring the structural safety and stability of the door and window.

Surface treatment layers: The testing scope covers all the functional and decorative coatings attached to the aluminium base materials. For example, the thicknesses and sealing qualities of the anodized films, the uniformity of the electrophoretic paint films, the impact resistance of the powder spraying coatings, and the UV resistance of the fluorocarbon spraying, etc. Each layer of the treatment needs to correspond to its specific quality standards.

Insulation materials: Specially referring to the thermal break strips (mostly the polyamide nylon PA66 with the glass fibers) used for the thermal break aluminium door and window. The testing scope includes their material compositions (preventing the PVC substitution), dimension precision, mechanical properties (transverse tensile strength and longitudinal shear strength), as well as the long-term heat resistance and aging resistance.

Connection and assembly parts: The testing scope extends to the key parts guaranteeing the integrity of the door and window, such as the corner codes, corner plates, fasteners (screws and bolts) and sealing rubber strips. Their materials (such as the stainless steel corner codes), strengths, corrosion resistance and dimension matching need to be tested, and they have the direct effects on the corner strengths and air tightness of the door and window.

Finished door and window performance related items: The scope of the material testing ultimately serves the performance of the finished door and window. For example, the rigidity of the profiles affects the wind load resistance, the dimension precision affects the air and water tightness, the surface treatment qualities affect the weather resistance, and the insulation material properties directly determine the thermal insulation performance. The testing needs to establish the relationships between the materials and system performances.

Testing Methods

Spectroscopic analysis method: Used for the chemical composition analysis, mainly adopting the spark discharge atomic emission spectrometry (OES). The profile samples are prepared into the smooth surfaces, and the characteristic spectra are generated through the electrode excitation. After the analysis by the dispersion systems and detectors, the quantitative results of the various elements can be quickly and accurately obtained. It is the necessary method of the raw material incoming inspection.

Tensile testing method: According to the GB/T 228.1 standard, the aluminium alloy profiles are machined into the tensile specimens of the specified shapes and sizes, and the axial tensile forces are applied at the constant rates on the universal material testing machines until the specimen fracture. Through the recorded load-displacement curves, the core mechanical parameters such as the tensile strength, yield strength and elongation are calculated.

Film thickness measurement method: The surface treatment layer thicknesses are the core control indicators. For the non-conductive coatings (such as the powder and fluorocarbon coatings), the eddy current thickness gauges are used; for the conductive films such as the anodized films, the eddy current method or metallographic microscope method (cross-section observation) can be used. The measurement needs to select the sufficiently many representative points on the profile surfaces.

Adhesion cross-cut testing method: According to the GB/T 9286 standard, the multi-blade cutting tools are used to scribe the grids of the specified spacings (such as 1mm×1mm) on the coating surfaces, and the scratches need to penetrate the coatings to the substrates. Then the dedicated tapes are adhered and quickly torn off, and the adhesion is evaluated according to the coating falling off proportions in the grid areas (grades 0-5). The lower the grade, the better the performance.

Salt spray testing method: The accelerated testing method of evaluating the corrosion resistance. The specimens are placed in the closed salt spray test chambers, continuously or intermittently sprayed with the sodium chloride solution of the specific concentration (such as 5%), creating the constant-temperature, high-humidity and high-salt corrosion environments. After the continuous spraying for a certain time (such as 1000 hours), the corrosion conditions of the specimen surfaces are observed and recorded.

Thermal break strip property testing method: The thermal break strips need to carry out the multiple tests. The transverse tensile strength testing simulates their stressed states in the profile cavities; the high-temperature lasting load testing evaluates their long-term heat deformation resistance; at the same time, the composition analysis (such as the differential scanning calorimetry DSC measuring the melting points) also needs to be carried out to identify whether it is the genuine PA66 GF25 material.

Testing Standards

Domestic Standards:

1. GB/T 5237.1, Wrought aluminium alloy extruded profiles for architecture — Part 1: Profiles without surface treatment

2. GB/T 5237.2, Wrought aluminium alloy extruded profiles for architecture — Part 2: Anodized profiles

3. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

4. GB/T 229-2020, Metallic materials — Charpy pendulum impact test method

5. GB/T 9286, Paints and varnishes — Cross-cut test

6. GB/T 230.1-2018, Metallic materials — Rockwell hardness test — Part 1: Test method

7. GB/T 10125-2021, Corrosion tests in artificial atmospheres — Salt spray tests

International Standards:

1. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

2. ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests

3. ISO 2409, Paints and varnishes — Cross-cut test

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Direct-reading spectrometer: The core equipment of the chemical composition analysis. The instrument integrates the excitation light sources, dispersion systems, detectors and data processing units, which can complete the quantitative analysis of up to more than twenty elements in the aluminium alloy within seconds, with the high precision and good repeatability. It is the key instrument of guaranteeing the material designation conformity.

Universal material testing machine: The main equipment of carrying out the mechanical property testing such as the tensile, compression and bending. Equipped with the high-precision force transducers and displacement extensometers, the computer control systems control the loading rates and collect the data in real time, automatically generating the stress-strain curves and test reports. It is the equipment of evaluating the profile strengths.

Coating thickness gauge: Divided into the magnetic thickness gauges (for the iron and steel substrates) and eddy current thickness gauges (for the non-ferrous metal substrates). The eddy current thickness gauges use the high-frequency electromagnetic fields generated by the probes to form the eddy currents in the conductor substrates, whose amplitudes are affected by the non-conductive coating thicknesses, thereby carrying out the non-destructive measurement. The portable equipment is widely applied in the on-site inspection.

Salt spray test chamber: The dedicated equipment of simulating the marine or industrial atmospheric corrosion environments. The chambers are made of the corrosion-resistant materials and equipped with the spraying systems, heating systems, saturated air barrels and automatic control systems, which can precisely control the test temperatures, salt mist sedimentation amounts and spraying cycles. It is the standardized equipment of evaluating the corrosion resistance of the materials and coatings.

Precision dimension measurement tools: Including the digital callipers/micrometers (measuring the wall thicknesses and shape dimensions), R gauges (measuring the transition arcs), feeler gauges (measuring the assembly clearances), platforms and dial indicators (measuring the straightness and twist). For the complex cross-sections, the high-precision coordinate measuring machines (CMM) need to be used for the three-dimensional scanning and data analysis.

Thermal insulation property testing equipment: Mainly including the guarded hot plate method thermal conductivity instruments or heat flow meter method thermal conductivity instruments. The equipment is composed of the hot plates, cold plates, guard units and measurement systems. Through the establishment of the stable unidirectional heat flows, the heat flows and temperature differences through the specimens are measured, thereby precisely calculating the thermal conductivity (λ values) of the insulation materials or composite profiles.