Views: 0 Author: Site Editor Publish Time: 2026-09-25 Origin: Site
In modern industries – aerospace, shipbuilding, petrochemicals, power station boilers, new energy vehicles, 3C electronics, power batteries, medical devices, and more – the application of dissimilar material welding is becoming increasingly widespread. Joining different metallic materials enables maximum utilisation of each material’s performance advantages, optimises structural design, and reduces the use of expensive materials – effectively lowering production costs.
However, dissimilar material welding is also the most technically challenging issue in the welding field. When two metals with vastly different physical and chemical properties are brought together at high temperatures – differences in melting point, coefficient of thermal expansion, and thermal conductivity all converge – creating significant risks to weld quality.
Quality control for dissimilar material welding is not an isolated technical operation – it is a full-process systems engineering effort covering filler metal selection, procedure design, process control, and inspection verification. This article starts from the challenges of dissimilar welding and systematically explains the key quality control points throughout the entire process.
Understanding why dissimilar material welding is difficult is the first step in establishing an effective quality control system. The difficulties are mainly reflected in the following aspects:
Physical Property Difference | Problem During Welding | Consequence |
|---|---|---|
Different melting points | Low-melting material melts and flows away first, while high-melting material remains solid | Changes in weld composition, alloying element burn-off, difficult joint fusion |
Different coefficients of thermal expansion | Uneven expansion and contraction during the welding thermal cycle | Large welding stresses and distortion; cracking in severe cases |
Different thermal conductivity and specific heat | Heat propagates at different rates in the two materials | Severe grain coarsening in the weld metal; affects wettability of refractory metals |
Different laser absorptivity | Different absorption rates for the laser beam | Partial melting of the molten pool, unstable keyhole |
Dissimilar metal welding also faces a range of metallurgical issues that do not exist in same-material welding:
Non-uniform composition in the fusion zone: There are significant differences in composition between the base metals and filler on both sides. During welding, the base and filler metals mix, and the degree of mixing varies at different locations – creating chemical heterogeneity
Carbon migration: During post-weld heat treatment or high-temperature service, carbon migrates from the low-alloy side toward the higher-alloy weld metal, forming decarburised and carburised layers on either side of the fusion line. The decarburised zone has degraded properties and is prone to premature failure during service
Martensitic transition zone: Between an austenitic weld and a pearlitic base metal, there is a high-hardness, brittle martensitic transition zone with low toughness – a weak region prone to failure
Intermetallic compounds (IMC): Hard, brittle intermetallic layers tend to form at the interface of dissimilar metals. When the IMC layer exceeds 10 microns, the structural integrity of the joint is seriously compromised
Dissimilar metal joints are mainly divided into three categories:
Combination Type | Typical Examples | Main Welding Problems |
|---|---|---|
Dissimilar steels | Pearlitic + austenitic steels, clad steels | Non-uniform weld chemistry, reduced plasticity in the fusion zone (brittle layer), stress cracking |
Steel + non-ferrous metals | Steel + aluminium, steel + copper | Lack of fusion due to oxidation, porosity, cracks, degraded joint mechanical properties |
Dissimilar non-ferrous metals | Copper + aluminium, aluminium + titanium | Lack of fusion due to oxidation, brittle phases, porosity, cracks |
Filler metal selection is the foundation of quality control in dissimilar material welding.
Filler selection principles for dissimilar steel welding:
Base Material Combination | Recommended Filler | Selection Basis |
|---|---|---|
Carbon steel + stainless steel (304/316) | 309L (preferred) | Alloy content sufficient to balance dilution |
Carbon steel + stainless (high Cr demand) | 312 | For applications requiring higher chromium |
Carbon steel + Mo-bearing stainless | 309Mo | Molybdenum-containing version for improved corrosion resistance |
Austenitic + austenitic (304+316) | Match the higher-alloy base metal (316 type) | “Follow the higher” principle |
Core principles:
For dissimilar material welding, select filler metal according to the base metal with the higher alloy content
For base metals with higher C, S, P impurities, choose electrodes with better crack resistance and porosity resistance
When welding duplex stainless steel to 304 stainless steel or nickel alloys, special attention must be paid to critical variables such as ferrite balance, wire selection, solidification cracking, and cooling rate
Most welding methods can be used for dissimilar metal welding, each with its own advantages and disadvantages:
Fusion welding methods: SMAW, SAW, GMAW, GTAW, PAW, EBW, LBW, etc. are widely used for dissimilar metal welding
High-energy-density heat sources: To reduce dilution and fusion ratio, methods with higher energy density – such as electron beam welding, laser welding, and plasma arc welding – are often preferred
Pressure welding methods: For specific combinations that are difficult to fusion weld, pressure welding methods may be used
Procedure qualification requirements for dissimilar material welding are more stringent than for similar materials. Key standards include ISO 15614-1:2017 and ISO 15614-12:2021:
For dissimilar steel welding procedure qualification test pieces, impact testing must be performed on both the weld metal and the heat-affected zones on both sides
The scope and number of tests for dissimilar steel welding qualification shall comply with relevant specifications
Dissimilar steel welding in the petrochemical industry must follow specialised standards such as SH/T 3526
Procedure qualification for welds with buttering layers has additional specific requirements
In dissimilar material welding, heat input control precision requirements are far more stringent than in similar-material welding.
Take steel-aluminium laser welding as an example:
Steel melting point: approximately 1500°C
Aluminium melting point: approximately 660°C
Thermal conductivity of aluminium is approximately 4-5 times that of steel
If the heat source is centred on the weld centreline, the aluminium side acts like a giant heatsink drawing heat away, while the steel side becomes overheated. This asymmetry leads to uneven penetration and the formation of brittle Fe-Al intermetallic layers.
Key points of heat input control:
Laser beam offset welding is an effective method for controlling the interfacial microstructure in dissimilar metal welds – offsetting the laser beam 0.1–0.2mm toward the steel side can minimise macro-segregation and eliminate the softened transition zone
Weld penetration fluctuations should be controlled within 0.2mm
Welding distortion can be controlled within 1.5mm/m
Thermal imaging technology has become a critical tool for quality control in dissimilar material welding:
Real-time monitoring of asymmetric heat distribution: Thermal cameras capture two-dimensional temperature maps of the entire weld zone, detecting whether the arc or laser beam has drifted toward the more thermally conductive metal
Cooling rate (t8/5) analysis: The cooling time from 800°C to 500°C determines the final microstructure. Thermal imaging monitors cooling rates on both sides of the weld simultaneously, detecting deviations in real time
Cold defect detection in highly conductive metals: Copper and aluminium cool rapidly – prone to “cold starts” and lack of fusion
In any fusion weld, some base metal melts into the weld pool, causing dilution:
Process measures such as indirect arc, oscillating wire, and strip electrodes can reduce penetration depth
Controlling and shortening the residence time of metal in the liquid or high-temperature solid state can mitigate detrimental effects such as intermetallic compound formation
For Magnetic Pulse Welding (MPW) and other pressure welding processes, the risk of intermetallic compounds can be significantly reduced
Non-destructive testing of dissimilar metal welded joints must be selected based on the material combination and service conditions:
Method | Detection Object | Applicable Scenarios |
|---|---|---|
Radiographic Testing (RT) | Internal porosity, inclusions, lack of fusion | Dissimilar steels, steel-non-ferrous welds |
Ultrasonic Testing (UT) | Internal cracks, delamination, lack of fusion | Thick-section dissimilar joints |
Penetrant Testing (PT) | Surface-breaking defects | Non-magnetic dissimilar materials |
Magnetic Particle Testing (MT) | Surface and near-surface defects | Ferromagnetic dissimilar materials |
Tensile testing: Verifies whether joint strength meets design requirements
Bend testing: Verifies joint ductility and toughness
Hardness testing: Detects abnormal hardened layers in the fusion zone
Metallographic examination: Evaluates intermetallic compound layer thickness, degree of carbon migration, and microstructure
Depending on service conditions, dissimilar welded joints may also require:
High-temperature creep testing
Stress-rupture testing
Corrosion performance testing
Impact toughness testing (especially for low-temperature service)
Defect Type | Main Cause | Preventive Measures |
|---|---|---|
Welding cracks | Stress caused by differential thermal expansion | Buttering layer welding, thermal stress relief techniques, reduce dilution |
Porosity | Lack of fusion due to oxidation | Thorough cleaning, optimise shielding gas, control heat input |
Intermetallic compounds (IMC) | Reaction at the interface between two metals | Control heat input, control cooling rate, keep IMC layer <10μm |
Carbon migration | Carbon diffuses toward high-alloy side at high temperature | Use stabilised consumables, control post-weld heat treatment |
Non-uniform chemical composition | Uneven mixing of base and filler metals | Optimise welding parameters, select appropriate filler metal |
Quality control for dissimilar material welding cannot be solved by a single “magic parameter.” It is a full-process systems engineering effort covering filler metal selection, procedure design, process control, and inspection verification.
Summary of core principles:
Correct filler selection is the prerequisite – select filler metal according to the higher-alloy base material
Procedure qualification is the basis – dissimilar welding must undergo rigorous PQR
Heat input is the core variable – too high creates brittle IMC; too low causes lack of fusion
Real-time monitoring is the safeguard – online monitoring technologies such as thermal imaging detect deviations promptly
Inspection verification closes the loop – dual verification through NDT and destructive testing
When these five elements form a closed loop, the quality of dissimilar material welding ceases to be a gamble – it becomes a predictable, repeatable, and verifiable engineering capability.
“Quality in dissimilar material welding begins with correct filler selection, is achieved through precise process control, and is verified by rigorous inspection – every step is indispensable.”
