How to judge the quality of titanium fasteners?
1. Material certification (the most critical document):
Original Material Report: The supplier is required to provide a Mill Test Certificate (MTC) issued by the titanium material manufacturer. Verify:
Brand: Whether it is the agreed brand (such as pure titanium TA1/TA2, titanium alloy TC4/TC6/GR5, etc.).
Chemical composition: Whether the content of all elements (especially the main elements Al, V, Fe, O, etc.) is within the standard range.
Mechanical properties: Whether the tensile strength, yield strength, elongation, etc. meet the standards.
Traceability: The furnace batch number on the report should correspond to the raw material batch number.
2. Product standards and certifications:
Compliance with standards: The product is produced according to which standard (such as national standard GB/T, national military standard GJB, American standard ASTM, aviation standard HB, automotive standard, etc.). The standard defines performance thresholds.
System certification: Does the manufacturer have ISO 9001 quality system certification. Is there a higher-level certification such as AS9100, IATF 16949, ISO 13485 for special fields such as aerospace and medical.
3. Factory Inspection Report (COA):
Request to provide the 'Factory Inspection Report' for the same batch of products to see if key items (size, hardness, tensile strength, etc.) have been tested and if the data is qualified.
4. Vision and Touch:
Color and luster: The natural color of titanium alloy should be a uniform dark gray or silver gray. The color after anodizing should be uniform and consistent, without flower spots or color differences. The surface should be clean, free of oil stains and residual metal shavings.
Surface quality: Key parts such as threads and flange surfaces should be free of burrs, cracks, scratches, and bumps. This is particularly important for fasteners that withstand alternating stress.
Logo and identification: Whether the head logo (such as performance level, factory logo) is clear and correct.
5. Size and accuracy:
Key dimensions: Use tools such as calipers and micrometers to measure screw diameter, head size, flange thickness, etc., to see if they meet the drawing or standard tolerances.
Thread accuracy: Use a thread gauge to check. The GO gauge should be able to be smoothly screwed in, and the NO-GO gauge should not be screwed in more than 2-3 turns. This is the most basic and important assembly inspection.
6. Mechanical performance testing (verifying strength):
Hardness testing: measured using a Rockwell or Vickers hardness tester, the hardness value should be within a reasonable range corresponding to the material grade and heat treatment state. Hardness is an indirect reflection of strength and heat treatment effect.
Tensile/Wedge Load Test: Conducted on a universal material testing machine, this is the most direct strength verification. The test results (tensile strength, yield strength) must meet or exceed the standard requirements. The fracture location should be observed at the screw, not at the root of the thread (poor thread processing quality can lead to stress concentration).
7. Corrosion resistance test:
Salt spray test: Place the sample in a salt spray chamber and test it for the specified time (such as 96 hours, 240 hours) to observe whether there is red rust, white rust, or corrosion pits on the surface. Titanium alloys theoretically have excellent resistance to salt spray, but surface treatment defects can lead to localized corrosion.